GH Actions: set error reporting to E_ALL

Turns out the default setting for `error_reporting` used by the SetupPHP action is `error_reporting=E_ALL & ~E_DEPRECATED & ~E_STRICT` and `display_errors` is set to `Off`.

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

.github/workflows/continuous-integration.yml

@@ -76,7 +76,7 @@ jobs:
         with:
           coverage: "none"
           extensions: "intl, zip"
-          ini-values: "memory_limit=-1, phar.readonly=0"
+          ini-values: "memory_limit=-1, phar.readonly=0, error_reporting=E_ALL, display_errors=On"
           php-version: "${{ matrix.php-version }}"
           tools: composer
 

.github/workflows/lint.yml

@@ -29,7 +29,7 @@ jobs:
         with:
           coverage: "none"
           extensions: "intl"
-          ini-values: "memory_limit=-1"
+          ini-values: "memory_limit=-1, error_reporting=E_ALL, display_errors=On"
           php-version: "${{ matrix.php-version }}"
 
       - name: "Lint PHP files"