CI: switch to GitHub Actions - step 3: move the PEAR package validation

The PEAR native package validation script used to be run on every PHP build, but the results should be no different on any particular PHP version.

To that end, move the running of the script from the "test" cycles, to the one-time only run PEAR specific job.

Author: jrfnl

.github/workflows/validate.yml

@@ -71,3 +71,6 @@ jobs:
 
       - name: Validate the PEAR package file contents
         run: php scripts/validate-pear-package.php
+
+      - name: Validate the PEAR package
+        run: pear package-validate package.xml

.travis.yml

@@ -64,7 +64,6 @@ script:
   - php bin/phpcs --config-set php_path php
   - vendor/bin/phpunit tests/AllTests.php
   - php bin/phpcs --no-cache --parallel=1
-  - pear package-validate package.xml
   - composer validate --no-check-all --strict
   - php scripts/build-phar.php
   - php phpcs.phar