GH Actions: turn error reporting on

The default ini file used by the SetupPHP action is the production one, which turns error_reporting/display off.

For the purposes of CI, I'd recommend running with `error_reporting=-1` and `display_errors=On` to ensure **all** PHP notices are shown.

Also see: shivammathur/setup-php#469

.github/workflows/build.yml

@@ -41,6 +41,7 @@ jobs:
         with:
           coverage: "none"
           php-version: "${{ matrix.php-version }}"
+          ini-values: error_reporting=-1, display_errors=On, zend.assertions=1
 
       - name: "Reset composer platform"
         if: matrix.php-version == '7.2' || matrix.php-version == '7.3' || matrix.php-version == '7.4'
@@ -77,6 +78,7 @@ jobs:
         with:
           coverage: "none"
           php-version: "${{ matrix.php-version }}"
+          ini-values: error_reporting=-1, display_errors=On, zend.assertions=1
 
       - name: "Install dependencies"
         uses: "ramsey/composer-install@v2"
@@ -152,6 +154,7 @@ jobs:
           coverage: "none"
           php-version: "${{ matrix.php-version }}"
           extensions: mbstring
+          ini-values: error_reporting=-1, display_errors=On, zend.assertions=1
 
       - name: "Reset composer platform"
         if: matrix.php-version == '7.2' || matrix.php-version == '7.3' || matrix.php-version == '7.4' || matrix.php-version == '8.0'
@@ -188,6 +191,7 @@ jobs:
         with:
           coverage: "pcov"
           php-version: "${{ matrix.php-version }}"
+          ini-values: error_reporting=-1, display_errors=On, zend.assertions=1
 
       - name: "Install dependencies"
         uses: "ramsey/composer-install@v2"