Update github workflow to install dev packages for phpstan

Author: norkunas

.github/workflows/main.yml

@@ -8,6 +8,8 @@ jobs:
             - uses: actions/checkout@master
             - name: PHPStan
               uses: docker://oskarstark/phpstan-ga
+              env:
+                  REQUIRE_DEV: true
               with:
                   args: analyze --no-progress