Target lockfile update PR to source branch

Fixes #961

.github/workflows/conda-lock.yml

@@ -73,21 +73,43 @@ jobs:
           private-key: ${{ secrets.AUTH_APP_PRIVATE_KEY }}
 
       - name: Create pull requests
+        env:
+          source_ref: ${{ github.ref }}
+          source_ref_type: ${{ github.ref_type }}
         run: |
           shopt -s globstar
+
+          # Display any changes in the log.
           git diff --name-status
-          if $(sha256sum --status -c ${{ runner.temp }}/lock_file_hashes); then
+
+          # Exit early if there are no changes.
+          if $(sha256sum --status -c ${{ runner.temp }}/lock_file_hashes)
+          then
             echo "Lock files unchanged. Skipping pull request..."
             exit 0
           fi
-          # Update lock_file_hashes so pushed branch name is unique.
-          sha256sum **/locks/*.txt > ${{ runner.temp }}/lock_file_hashes
+
+          # Commit changed lockfiles.
           git add **/locks/*.txt
           git commit -m "[CI] Update conda lock files"
+
+          # Update lock_file_hashes so pushed branch name is unique.
+          sha256sum **/locks/*.txt > ${{ runner.temp }}/lock_file_hashes
           remote_branch_name="conda-lock-$(sha256sum ${{ runner.temp }}/lock_file_hashes | head -c 8)"
+
+          # If running from a branch target the created PR at that branch.
+          if [[ $source_ref_type = branch ]]
+          then
+            base_branch_name="$source_ref"
+          else
+            base_branch_name="main"
+          fi
+
+          # Push branch to GitHub.
           git push --set-upstream origin "conda-lock-files:${remote_branch_name}"
+
           # Create PR on GitHub using GitHub REST API.
-          request_body='{"title":"[CI] Update conda lock files","body":"Created automatically by GitHub Actions.","base":"main","head":"'"${remote_branch_name}"'"}'
+          request_body='{"title":"[CI] Update conda lock files","body":"Created automatically by GitHub Actions.","base":"'"${base_branch_name}"'","head":"'"${remote_branch_name}"'"}'
           curl -LsS --fail-with-body \
             -X POST \
             -H "Accept: application/vnd.github+json" \