chore: publish mainline snap releases to stable channel (#190)

Author: matifali

.github/workflows/publish-snaps.yaml

@@ -59,10 +59,12 @@ jobs:
 
       - uses: snapcore/action-build@v1
         id: build
+        if: ${{ steps.metadata.outputs.release_channel == 'mainline' }}
 
       - uses: snapcore/action-publish@v1
+        if: ${{ steps.metadata.outputs.release_channel == 'mainline' }}
         env:
           SNAPCRAFT_STORE_CREDENTIALS: ${{ secrets.SNAPCRAFT_TOKEN }}
         with:
           snap: ${{ steps.build.outputs.snap }}
-          release: ${{ steps.metadata.outputs.release_channel }}
+          release: stable