Checkout base branch

(cherry picked from commit aa140f5)

Author: jslee02

.github/workflows/update_lockfiles.yml

@@ -17,6 +17,8 @@ jobs:
         base: [main, release-6.14]
     steps:
       - uses: actions/checkout@v4
+        with:
+          ref: ${{ matrix.base }}
       - name: Set up pixi
         uses: prefix-dev/setup-pixi@v0.8.1
         with: