[CLN] Turn PR title checker back on :/ (#1768)

## Description of changes

*Summarize the changes made by this PR.*
 - Improvements & Bug fixes
- Turn PR title checker back on. I accidentally disabled it by munging
the regex

## Test plan
*How are these changes tested?*

- [ ] Tests pass locally with `pytest` for python, `yarn test` for js

## Documentation Changes
*Are all docstrings for user-facing APIs updated if required? Do we need
to make documentation changes in the [docs
repository](https://github.com/chroma-core/docs)?*

.github/workflows/check-pr-title.yml

@@ -13,7 +13,7 @@ jobs:
         - name: Check PR Title
           uses: Slashgear/[email protected]
           with:
-            regexp: '[(ENH|BUG|DOC|TST|BLD|PERF|TYP|CLN|CHORE)].*'
+            regexp: '\[(ENH|BUG|DOC|TST|BLD|PERF|TYP|CLN|CHORE)\].*'
             helpMessage: "Please tag your PR title. See https://docs.trychroma.com/contributing#contributing-code-and-ideas"
         - name: Comment explaining failure
           if: failure()