Bugfix: Restore stale workflow functionality

The stale workflows are currently failing with the error:

    Invalid workflow file: .github/workflows/stale.yml#L26
    The workflow is not valid. .github/workflows/stale.yml (Line: 26, Col: 11): A sequence was not expected

To fix this, the list of exempt-issues-labels in .github/workflows/stale.yml
must be a  comma separated list. A single quote is placed around the list to
allow for use of colons in label names.

Signed-off-by: Melissa Sulprizio <mpayer@seas.harvard.edu>

.github/workflows/stale.yml

@@ -22,7 +22,7 @@ jobs:
       with:
         repo-token: ${{ secrets.GITHUB_TOKEN }}
         stale-issue-label: 'stale'
-        exempt-issue-labels: ['category: Discussion','category: Feature Request','deferred','help needed: Open Research Problem','help needed: Request Input from Community','never stale','TODO: Documentation']
+        exempt-issue-labels: 'category: Discussion,category: Feature Request,deferred,help needed: Open Research Problem,help needed: Request Input from Community,never stale,TODO: Documentation'
         days-before-issue-stale: 30
         days-before-issue-close: 7
         stale-issue-message: 'This issue has been automatically marked as stale because it has not had recent activity. If there are no updates within 7 days it will be closed. You can add the "never stale" tag to prevent the issue from closing this issue.'

CHANGELOG.md

@@ -43,6 +43,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
   to`PHOTOL(168:177)`
 - Updated `Jval_` entries in `run/GCHP/HISTORY.rc.templates/HISTORY.rc.fullchem`
 - Updated species database Is_Photolysis entries to remove J-value diagnostics with all zeros in full chemistry simulation
+- Fixed formatting error in `.github/workflows/stale.yml` that caused the Mark Stale Issues action not to run
 
 ## [14.4.3] - 2024-08-13
 ### Added