update labeler.yml for labeler v5

[braingram]

labeler v5 introduced breaking changes for the config file format.

This PR updates the config to the new format.

As the workflow that uses this action runs on pull_request_target the CI run for this PR will not reflect the config file changes in this PR (the config file will be pulled from the main branch). To test this PR I opened a test PR against the source branch for this PR with some changes that should trigger labels.
braingram#1
The labeler action on the test PR ran without errors and labels were applied:
https://github.com/braingram/jwst/actions/runs/7159251698/job/19492299084?pr=1

Checklist for maintainers

• added entry in CHANGES.rst within the relevant release section
• updated or added relevant tests
• updated relevant documentation
• added relevant milestone
• added relevant label(s)
• ran regression tests, post a link to the Jenkins job below.
  How to run regression tests on a PR
• Make sure the JIRA ticket is resolved properly

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (b8e85bd) 75.32% compared to head (5466e12) 75.32%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #8117   +/-   ##
=======================================
  Coverage   75.32%   75.32%           
=======================================
  Files         464      464           
  Lines       38002    38002           
=======================================
  Hits        28626    28626           
  Misses       9376     9376           

Flag	Coverage Δ		*Carryforward flag
nightly	77.37% <ø> (ø)		Carriedforward from b8e85bd

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[hbushouse]

LGTM