chore: add condition for only building on main

ensure that longer-to-build images only get built on main

.github/workflows/build.yml

@@ -29,8 +29,10 @@ jobs:
       - uses: actions/checkout@8ade135a41bc03ea155e62e844d188df1ea18608 # v4.1.0
       - uses: GeoNet/yq@bbe305500687a5fe8498d74883c17f0f06431ac4 # master
       - id: set
+        env:
+          REF: ${{ github.ref }}
         run: |
-          echo "matrix-docker=$(jq -rMc '.build[] | select(.source | contains("Dockerfile")) | . as $config | .destination | capture("(?<registry>.*)/(?<imageName>.*):(?<tag>.*)") | . as $imgSplit | $config | .source | capture("(?<context>.*)/Dockerfile") | . as $context | $config + $imgSplit + $context' -r -c <<< "$(yq e . -o json config.yaml)" | jq -rcsM '{"include":.}')" >> $GITHUB_OUTPUT
+          echo "matrix-docker=$(jq --arg REF "$REF" -rMc '.build[] | select(.source | contains("Dockerfile")) | select(.buildOnMain == null or $REF == "refs/heads/main") | . as $config | .destination | capture("(?<registry>.*)/(?<imageName>.*):(?<tag>.*)") | . as $imgSplit | $config | .source | capture("(?<context>.*)/Dockerfile") | . as $context | $config + $imgSplit + $context' -r -c <<< "$(yq e . -o json config.yaml)" | jq -rcsM '{"include":.}')" >> $GITHUB_OUTPUT
           echo "matrix-apko=$(jq -rMc '.build[] | select(.source | contains("image.yaml"))' -r -c <<< "$(yq e . -o json config.yaml)" | jq -rcsM '{"include":.}')" >> $GITHUB_OUTPUT
       - name: check output
         run: |

config.yaml

@@ -86,7 +86,10 @@ build:
     destination: ghcr.io/geonet/base-images/chart-centos7:latest
   - source: ./images/rpmbuild-centos7/Dockerfile
     destination: ghcr.io/geonet/base-images/rpmbuild-centos7:latest
+    buildOnMain: true
   - source: ./images/rpmbuild-centos-stream8/Dockerfile
     destination: ghcr.io/geonet/base-images/rpmbuild-centos-stream8:latest
+    buildOnMain: true
   - source: ./images/rpmbuild-centos-stream9/Dockerfile
     destination: ghcr.io/geonet/base-images/rpmbuild-centos-stream9:latest
+    buildOnMain: true