ci: Allow testing PRs targetting release branches (#83)

Author: rm3l

.github/workflows/test.yml

@@ -60,7 +60,7 @@ jobs:
           helm repo update
 
       - name: Run chart-testing (lint)
-        run: ct lint --config ct.yaml --helm-extra-args="--set upstream.backstage.image.tag=latest --set global.clusterRouterBase=app.example.yaml"
+        run: ct lint --config ct.yaml --target-branch ${{ github.event.pull_request.base.ref }} --helm-extra-args="--set upstream.backstage.image.tag=latest --set global.clusterRouterBase=app.example.yaml"
 
       - name: Create KIND Cluster
         uses: helm/kind-action@a1b0e391336a6ee6713a0583f8c6240d70863de3 # v1.12.0
@@ -83,7 +83,7 @@ jobs:
 
       - name: Run chart-testing (latest)
         # test with latest stable backstage-showcase release
-        run: ct install --config ct-install.yaml --helm-extra-set-args="--set=upstream.backstage.image.tag=latest --set=global.clusterRouterBase=app.example.com"
+        run: ct install --config ct-install.yaml --target-branch ${{ github.event.pull_request.base.ref }} --helm-extra-set-args="--set=upstream.backstage.image.tag=latest --set=global.clusterRouterBase=app.example.com"
   test-next:
     name: Test Next Release
     runs-on: ubuntu-latest
@@ -113,7 +113,7 @@ jobs:
           helm repo update
 
       - name: Run chart-testing (lint)
-        run: ct lint --config ct.yaml --helm-extra-args="--set upstream.backstage.image.tag=next --set global.clusterRouterBase=app.example.yaml"
+        run: ct lint --config ct.yaml --target-branch ${{ github.event.pull_request.base.ref }} --helm-extra-args="--set upstream.backstage.image.tag=next --set global.clusterRouterBase=app.example.yaml"
 
       - name: Create KIND Cluster
         uses: helm/kind-action@a1b0e391336a6ee6713a0583f8c6240d70863de3 # v1.12.0
@@ -136,4 +136,4 @@ jobs:
 
       - name: Run chart-testing (next)
         # test with the next backstage-showcase version (main branch)
-        run: ct install --config ct-install.yaml --helm-extra-set-args="--set=upstream.backstage.image.tag=next --set=global.clusterRouterBase=app.example.com"
+        run: ct install --config ct-install.yaml --target-branch ${{ github.event.pull_request.base.ref }} --helm-extra-set-args="--set=upstream.backstage.image.tag=next --set=global.clusterRouterBase=app.example.com"

ct.yaml

@@ -2,4 +2,3 @@ chart-dirs:
   - charts
 validate-maintainers: false
 remote: origin
-target-branch: main