Fixed creating release branches

- we didn't clone the repo at the point when we were running a git
  command, so that failed
- switched to a different method of checking out `main` and then
  checking out the most recent tag

.github/workflows/create-release-branch.yml

@@ -20,7 +20,7 @@ jobs:
   create-branch:
     runs-on: ubuntu-latest
     steps:
-      - run: echo "BASE_REF=$(git describe --tags --abbrev=0)" >> $GITHUB_ENV
+      - run: echo "BASE_REF=main" >> $GITHUB_ENV
         if: inputs.base-ref == 'latest'
 
       - run: echo "BASE_REF=${{ inputs.base-ref }}" >> $GITHUB_ENV
@@ -32,6 +32,10 @@ jobs:
           fetch-depth: 0
           submodules: true
 
+      - name: Checkout most recent tag
+        run: git checkout $(git describe --tags --abbrev=0)
+        if: inputs.base-ref == 'latest'
+
       - uses: asdf-vm/actions/install@v1
         with:
           tool_versions: |