build: allow v2 into APT candidate channel

.github/workflows/build-syncthing.yaml

@@ -875,9 +875,7 @@ jobs:
       - name: Prepare packages
         run: |
           kind=stable
-          if [[ $VERSION == v2* ]] ; then
-            kind=v2
-          elif [[ $VERSION == *-rc.[0-9] ]] ; then
+          if [[ $VERSION == *-rc.[0-9] || $VERSION == *-rc.[0-9][0-9] ]] ; then
             kind=candidate
           elif [[ $VERSION == *-* ]] ; then
             kind=nightly