Added support for latest when creating release branches

- this should allow us to run the job without any manual effort, because
  it'll choose the latest tag for the patch release

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

@@ -3,11 +3,12 @@ on:
   workflow_dispatch:
     inputs:
       base-ref:
-        description: 'Git ref to base from'
+        description: 'Git ref to base from (defaults to latest tag)'
         type: string
+        default: 'latest'
         required: false
       bump-type:
-        description: ''
+        description: 'Version bump type (patch, minor)'
         type: string
         required: false
         default: 'patch'
@@ -19,9 +20,15 @@ jobs:
   create-branch:
     runs-on: ubuntu-latest
     steps:
+      - run: echo "BASE_REF=$(git describe --tags --abbrev=0)" >> $GITHUB_ENV
+        if: inputs.base-ref == 'latest'
+
+      - run: echo "BASE_REF=${{ inputs.base-ref }}" >> $GITHUB_ENV
+        if: inputs.base-ref != 'latest'
+
       - uses: actions/checkout@v3
         with:
-          ref: ${{ inputs.base-ref }}
+          ref: ${{ env.BASE_REF }}
           fetch-depth: 0
           submodules: true