Change Windows test mode from 'latest' to 'stable' (JuliaMolSim#1151)

Probably a copy/paste mistake when I changed how the test matrix is produced...

Author: Technici4n

.github/workflows/ci.yaml

@@ -33,7 +33,7 @@ jobs:
       - if: ${{ github.event_name != 'pull_request' }}
         run: |
           cat >> matrix.yaml <<- EOM
-          - {mode: latest,  arch: x64,     os: windows-latest, payload: minimal          }
+          - {mode: stable,  arch: x64,     os: windows-latest, payload: minimal          }
           EOM
       - name: Convert to JSON
         run: |