Add glob to have review syntax highlight flow.cylc(.processed) files.

[wxtim]

These changes partially address #4261 : Cylc Review is not identifying flow.cylc and flow.cylc.processed as files to be syntax highlighted.

• I have read CONTRIBUTING.md and added my name as a Code Contributor.
• Contains logically grouped changes (else tidy your branch by rebase).
• Does not contain off-topic changes (use other PRs for other changes).
• Applied any dependency changes to both setup.py and
  conda-environment.yml.
• Manual testing only: Legacy Software. To test check that cylc.flow and cylc.flow.processed are highlighted.
• No change log entry: Will add a changelog entry covering all parts of Review: Small Bugs Meta Issue #4261
• No documentation update required.

I think that this needs only 1 review.

[hjoliver]

👍