ci: move prev version and tag message after switch

.forgejo/workflows/build.yaml

@@ -29,11 +29,11 @@ jobs:
 
       - name: Commit build
         run: |
-          previous_version=$(git describe --tags --abbrev=0 2>/dev/null || echo '')
           current_version=v$(cat package.json | grep version | grep -o -E '([0-9]+\.){2}[0-9]+')
-          tag_message=`git log --pretty='format:%s' $previous_version..`
 
           git switch build
+          previous_version=$(git describe --tags --abbrev=0 2>/dev/null || echo '')
+          tag_message=`git log --pretty='format:%s' $previous_version..`
 
           shopt -s extglob
           shopt -s dotglob