CI: switch to GitHub Actions - step 2: XML and PEAR validation

This commit:
* Adds a GH  Actions workflow for the build which validated the XML file against schema and checked their code style consistency, as well as validate the PEAR package file, as was previously run on Travis.
*  Removes that part of the `.travis.yml` configuration.

Notes:
Builds will run on all pushes and on pull requests, with the exception  of those just modifying files which are irrelevant to this workflow.

Author: jrfnl

.github/workflows/validate.yml

@@ -0,0 +1,73 @@
+name: Validate
+
+on:
+  # Run on all pushes and on all pull requests.
+  # Prevent the build from running when there are only irrelevant changes.
+  push:
+    paths-ignore:
+      - '**.md'
+  pull_request:
+    paths-ignore:
+      - '**.md'
+
+jobs:
+  checkxml:
+    name: Check XML files
+    runs-on: ubuntu-latest
+
+    env:
+      XMLLINT_INDENT: '    '
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
+
+      - name: Install xmllint
+        run: sudo apt-get install --no-install-recommends -y libxml2-utils
+
+      - name: Retrieve XML Schema
+        run: curl -O https://www.w3.org/2012/04/XMLSchema.xsd
+
+      # Show XML violations inline in the file diff.
+      # @link https://github.com/marketplace/actions/xmllint-problem-matcher
+      - uses: korelstar/xmllint-problem-matcher@v1
+
+      # Validate the XML ruleset files.
+      # @link http://xmlsoft.org/xmllint.html
+      - name: Validate rulesets against schema
+        run: xmllint --noout --schema phpcs.xsd ./src/Standards/*/ruleset.xml
+
+      # Validate the XSD file.
+      # @link http://xmlsoft.org/xmllint.html
+      - name: Validate XSD against schema
+        run: xmllint --noout --schema ./XMLSchema.xsd ./phpcs.xsd
+
+      # Check the code-style consistency of the XML files.
+      - name: Check XML code style
+        run: |
+          diff -B ./phpcs.xml.dist <(xmllint --format "./phpcs.xml.dist")
+          diff -B ./src/Standards/Generic/ruleset.xml <(xmllint --format "./src/Standards/Generic/ruleset.xml")
+          diff -B ./src/Standards/MySource/ruleset.xml <(xmllint --format "./src/Standards/MySource/ruleset.xml")
+          diff -B ./src/Standards/PEAR/ruleset.xml <(xmllint --format "./src/Standards/PEAR/ruleset.xml")
+          diff -B ./src/Standards/PSR1/ruleset.xml <(xmllint --format "./src/Standards/PSR1/ruleset.xml")
+          diff -B ./src/Standards/PSR2/ruleset.xml <(xmllint --format "./src/Standards/PSR2/ruleset.xml")
+          diff -B ./src/Standards/PSR12/ruleset.xml <(xmllint --format "./src/Standards/PSR12/ruleset.xml")
+          diff -B ./src/Standards/Squiz/ruleset.xml <(xmllint --format "./src/Standards/Squiz/ruleset.xml")
+          diff -B ./src/Standards/Zend/ruleset.xml <(xmllint --format "./src/Standards/Zend/ruleset.xml")
+
+  pear:
+    name: "PHP: 7.4 | PEAR package validation"
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
+
+      - name: Install PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: '7.4'
+          coverage: none
+
+      - name: Validate the PEAR package file contents
+        run: php scripts/validate-pear-package.php

.travis.yml

@@ -46,36 +46,6 @@ jobs:
       - php bin/phpcs --config-set php_path php
       - vendor/bin/phpunit tests/AllTests.php
 
-    # Build running just the PEAR package file and XML file validation and code style check.
-    - php: 7.4
-      name: "PHP: 7.4 | Pear + XML validate"
-      addons:
-        apt:
-          packages:
-            - libxml2-utils
-      before_install:
-      - export XMLLINT_INDENT="    "
-      - phpenv config-rm xdebug.ini || echo 'No xdebug config.'
-      install:
-      - curl -O https://www.w3.org/2012/04/XMLSchema.xsd
-      script:
-      # Validate the Pear Package file contents.
-      - php scripts/validate-pear-package.php
-      # Validate the xml ruleset files.
-      # @link http://xmlsoft.org/xmllint.html
-      - xmllint --noout --schema phpcs.xsd ./src/Standards/*/ruleset.xml
-      - xmllint --noout --schema ./XMLSchema.xsd ./phpcs.xsd
-      # Check the code-style consistency of the xml files.
-      - diff -B ./phpcs.xml.dist <(xmllint --format "./phpcs.xml.dist")
-      - diff -B ./src/Standards/Generic/ruleset.xml <(xmllint --format "./src/Standards/Generic/ruleset.xml")
-      - diff -B ./src/Standards/MySource/ruleset.xml <(xmllint --format "./src/Standards/MySource/ruleset.xml")
-      - diff -B ./src/Standards/PEAR/ruleset.xml <(xmllint --format "./src/Standards/PEAR/ruleset.xml")
-      - diff -B ./src/Standards/PSR1/ruleset.xml <(xmllint --format "./src/Standards/PSR1/ruleset.xml")
-      - diff -B ./src/Standards/PSR2/ruleset.xml <(xmllint --format "./src/Standards/PSR2/ruleset.xml")
-      - diff -B ./src/Standards/PSR12/ruleset.xml <(xmllint --format "./src/Standards/PSR12/ruleset.xml")
-      - diff -B ./src/Standards/Squiz/ruleset.xml <(xmllint --format "./src/Standards/Squiz/ruleset.xml")
-      - diff -B ./src/Standards/Zend/ruleset.xml <(xmllint --format "./src/Standards/Zend/ruleset.xml")
-
   allow_failures:
     - php: nightly