infra: docker: fix workflow to always run on master

.gitea/workflows/gentoo-utils.yml

@@ -20,10 +20,14 @@ jobs:
       - name: Check for changes before building
         id: image-changes
         run: |
-          if git diff --name-only ${{ gitea.event.before }} ${{ gitea.sha }} | grep -q '^\.docker/'; then
-            echo "changes_detected=true" >> $GITEA_OUTPUT
+          if [[ ${{ gitea.ref_name }} == ${{ gitea.event.repository.default_branch }} ]]; then
+            echo "run_image_builder=true" >> $GITEA_OUTPUT
           else
-            echo "changes_detected=false" >> $GITEA_OUTPUT
+            if git diff --name-only ${{ gitea.event.before }} ${{ gitea.sha }} | grep -q '^\.docker/'; then
+              echo "run_image_builder=true" >> $GITEA_OUTPUT
+            else
+              echo "run_image_builder=false" >> $GITEA_OUTPUT
+            fi
           fi
       -
         name: Set up Docker buildx
@@ -41,7 +45,7 @@ jobs:
 
       -
         name: Build and push
-        if: steps.docker-changes.outputs.changes_detected == 'true'
+        if: steps.docker-changes.outputs.run_image_builder == 'true'
         uses: docker/build-push-action@v6
         with:
           push: true