infra: image: switch to using ${{ vars.REGISTRY_URL }}

Doing this so I can change this site wide in the future without anything breaking

.gitea/workflows/gentoo-utils.yml

@@ -32,7 +32,7 @@ jobs:
           if ! git diff ${{ gitea.event.before }} ${{ gitea.sha }} --no-patch --exit-code .docker; then
             build_image=true
           else
-            if ! docker manifest inspect git.epenguin.net/${{ gitea.repository }}:${image_tag} >/dev/null 2>&1; then
+            if ! docker manifest inspect ${{ vars.REGISTRY_URL }}/${{ gitea.repository }}:${image_tag} >/dev/null 2>&1; then
               build_image=true
             else
               build_image=false
@@ -49,7 +49,7 @@ jobs:
         if: steps.image-changes.outputs.build_image == 'true'
         uses: docker/login-action@v3
         with:
-          registry: git.epenguin.net
+          registry: ${{ vars.REGISTRY_URL }}
           username: ${{ vars.CI_BOT_USERNAME }}
           password: ${{ secrets.CI_BOT_TOKEN }}
 
@@ -58,7 +58,7 @@ jobs:
         uses: docker/build-push-action@v6
         with:
           push: true
-          tags: git.epenguin.net/${{ gitea.repository }}:${{ steps.image-changes.outputs.image_tag }}
+          tags: ${{ vars.REGISTRY_URL }}/${{ gitea.repository }}:${{ steps.image-changes.outputs.image_tag }}
           context: "{{defaultContext}}:.docker"
     outputs:
       image_tag: ${{ steps.image-changes.outputs.image_tag }}
@@ -67,7 +67,7 @@ jobs:
     runs-on: brutalisk
     needs: build-oci-image
     container:
-      image: git.epenguin.net/${{ gitea.repository }}:${{ needs.build-oci-image.outputs.image_tag }}
+      image: ${{ vars.REGISTRY_URL }}/${{ gitea.repository }}:${{ needs.build-oci-image.outputs.image_tag }}
     steps:
       - name: Checkout repo
         uses: actions/checkout@v5