ci: ignore auto-version-* branches in lint workflow

As discussed here, workflows cannot be triggered for PRs created by bot accounts.

peter-evans/create-pull-request#48

There are workarounds, but they involve more work than they're worth.
For now, let's assume that these auto-version- branches don't need to be
linted. They only make a single change to package.json, anyway.

.github/workflows/ci.yml

@@ -1,5 +1,8 @@
 name: CI
-on: pull_request
+on:
+  pull_request:
+    branches-ignore:
+      - "auto-version-*"
 jobs:
   ci:
     name: Run linter and formatter