do not set version when merging to a release branch

Author: adwk67

.github/workflows/build.yml

@@ -345,7 +345,8 @@ jobs:
           crate: cargo-edit
           bin: cargo-set-version
       - name: Update version if PR
-        if: ${{ github.event_name == 'pull_request' }}
+        # For PRs to be merged against a release branch, the version has already been set, in which case ignore this step.
+        if: ${{ github.event_name == 'pull_request' && github.ref == 'refs/heads/main' }}
         run: cargo set-version --offline --workspace 0.0.0-pr${{ github.event.pull_request.number }}
 
       # Recreate charts and publish charts and docker image. The "-e" is needed as we want to override the