Set issue dialect labels via Github Actions

[greg-finley]

Brief summary of the change made

Closes #3665

See the auto-labeled issues in my fork: https://github.com/greg-finley/sqlfluff/issues

Are there any other side effects of this change that we should be aware of?

No. Maybe it should search issue body also, but searching only the title seems to have less false positives.

Pull Request checklist

• Please confirm you have completed any of the necessary steps below.

• Included test cases to demonstrate any code changes, which may be one or more of the following:

  • .yml rule test cases in test/fixtures/rules/std_rule_cases.
  • .sql/.yml parser test cases in test/fixtures/dialects (note YML files can be auto generated with tox -e generate-fixture-yml).
  • Full autofix test cases in test/fixtures/linter/autofix.
  • Other.

• Added appropriate documentation for the change.

• Created GitHub issues for any relevant followup/future enhancements if appropriate.

[codecov]

Codecov Report

Merging #3666 (cff0b28) into main (39c3fe6) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##              main     #3666   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          176       176           
  Lines        13359     13359           
=========================================
  Hits         13359     13359           

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[alanmcruickshank]

Looks good!