[Fix] Fix Image Tags (#445)

Co-authored-by: Tim Lorsbach <tim@lorsba.ch>
Reviewed-on: enviPath/enviPy#445

.gitea/workflows/build-image.yaml

@@ -1,8 +1,7 @@
 name: Build Docker Image
 
-# Trigger manually or when a PR to main is completed.
+# Trigger when a PR to main/develop is completed.
 on:
-  workflow_dispatch:
   pull_request:
     branches:
       - main
@@ -12,7 +11,7 @@ on:
 
 jobs:
   build-and-push:
-    if: ${{ github.event_name == 'workflow_dispatch' || github.event.pull_request.merged == true }}
+    if: ${{ github.event.pull_request.merged == true }}
     runs-on: ubuntu-latest
     steps:
       # Fetch the repository content for the Docker build context.
@@ -32,19 +31,18 @@ jobs:
           password: ${{ secrets.CI_REGISTRY_PASSWORD }}
 
       # Generate image tags/labels:
-      # - main branch gets stable "envipy" and "latest" tags
-      # - every build gets an increasing build number tag
-      # - branch-prefixed commit SHA tag remains for traceability
+      # - PRs targeting main get "latest" and "main-sha"
+      # - PRs targeting develop get "dev" and "dev-sha"
       - name: Extract metadata
         id: meta
         uses: docker/metadata-action@v5
         with:
           images: git.envipath.com/envipath/envipy
           tags: |
-            type=raw,value=envipy,enable=${{ github.ref_name == 'main' }}
-            type=raw,value=latest,enable=${{ github.ref_name == 'main' }}
-            type=raw,value=build-${{ github.run_number }}
-            type=sha,prefix={{branch}}-
+            type=raw,value=latest,enable=${{ github.event.pull_request.base.ref == 'main' }}
+            type=sha,prefix=main-,enable=${{ github.event.pull_request.base.ref == 'main' }}
+            type=raw,value=dev,enable=${{ github.event.pull_request.base.ref == 'develop' }}
+            type=sha,prefix=dev-,enable=${{ github.event.pull_request.base.ref == 'develop' }}
 
       # Load SSH key so Docker can pull private git+ssh dependencies during build.
       - name: Setup SSH for private git dependencies