fix(ci): align setup-go with go.mod version

Use go-version-file so CI always matches each branch's go directive.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: loginx

.github/workflows/ci.yml

@@ -20,7 +20,7 @@ jobs:
       - name: Set up Go
         uses: actions/setup-go@v5
         with:
-          go-version: '1.21'
+          go-version-file: 'go.mod'
       - name: Run unit tests
         run: go test ./...
       - name: Run BDD tests
@@ -46,7 +46,7 @@ jobs:
       - name: Set up Go
         uses: actions/setup-go@v5
         with:
-          go-version: '1.21'
+          go-version-file: 'go.mod'
 
       - name: Determine version
         id: version
@@ -109,7 +109,7 @@ jobs:
       - name: Set up Go (for preseed tool)
         uses: actions/setup-go@v5
         with:
-          go-version: '1.21'
+          go-version-file: 'go.mod'
 
       - name: Generate changelog (for stable releases)
         if: startsWith(github.ref, 'refs/tags/v')