Fixed build arg syntax

Signed-off-by: Moritz Mazetti <moritz@matchory.com>

Author: Radiergummi

.github/workflows/docker.yaml

@@ -218,8 +218,8 @@ jobs:
           context: .
           file: ./${{ matrix.dockerfile }}
           target: ${{ matrix.stage }}
-          build-args:
-            PHP_VERSION: ${{ matrix.php-version }}
+          build-args: |
+            PHP_VERSION=${{ matrix.php-version }}
           platforms: linux/amd64,linux/arm64
           push: true
           tags: ${{ steps.meta.outputs.tags }}