Add php linting to the test step

Run php -l on all PHP files. This makes sure the files are at least
parsable by the current PHP version - not a comprehensive compatibility
test but a good first step.

Theoretically this could be it's own flow, but since we already have the
whole environment setup and in place and it makes no sense to run unit
tests when the files not even lint, it's simple to add it here.

Author: splitbrain

.github/workflows/test.yml

@@ -45,7 +45,10 @@ jobs:
       - name: Setup PHPUnit
         run: |
           php _test/fetchphpunit.php
-          cd _test
+
+      - name: Check Syntax
+        run: |
+          find ${{ steps.dokuwiki-env.outputs.dir }} -name '*.php' -print0 | xargs -0L1 php -l
 
       - name: Run PHPUnit
         run: |

README.md

@@ -58,7 +58,9 @@ Uses the `phpmatrix` action to create the appropriate strategy matrixes for test
 
 ### test.yml
 
-This workflow executes all unit tests that have been marked with the `@group plugin_example` annotation. The PHP and DokuWiki versions to be used are supplied as JSON via input variables.
+This workflow first checks all `php` files for syntax errors, then executes all unit tests that have been marked with the `@group plugin_example` annotation.
+
+The PHP and DokuWiki versions to be used are supplied as JSON via input variables.
 
 The workflow will run on every push and on pull requests.