[TASK] Do not run PHPStan with unstable PHP versions

To catch problems in our code and in in association with the used
libraries, we don't need to check with unstable PHP versions.

This also avoids failures that are unrelated to our code.

.github/workflows/continuous-integration.yml

@@ -231,23 +231,12 @@ jobs:
           - '8.1'
           - '8.2'
           - '8.3'
-          - 'latest'
         dependencies:
           - 'lowest'
           - 'stable'
           - 'highest'
         experimental:
           - false
-        include:
-          - php-version: 'nightly'
-            dependencies: 'lowest'
-            experimental: true
-          - php-version: 'nightly'
-            dependencies: 'stable'
-            experimental: true
-          - php-version: 'nightly'
-            dependencies: 'highest'
-            experimental: true
 
     steps:
       - name: Checkout
@@ -286,10 +275,6 @@ jobs:
         if: contains(matrix.dependencies, 'highest')
         run: composer config minimum-stability alpha
 
-      - name: Ignore platfrom requirements for nightly
-        if: ${{ matrix.php-version == 'nightly' }}
-        run: echo "COMPOSER_UPDATE_FLAGS=$COMPOSER_UPDATE_FLAGS --ignore-platform-reqs" >> $GITHUB_ENV
-
       - name: Install dependencies without deprecation rules
         run: |
           composer remove --dev phpstan/phpstan-deprecation-rules --no-update ${{ env.COMPOSER_FLAGS }}