chore(ci): Specify branch for update-flake-lock

Author: srid

.github/workflows/update-flake-lock-doc.yaml

@@ -19,4 +19,5 @@ jobs:
           pr-title: "Update doc/flake.lock"
           pr-labels: |
             automated
-          path-to-flake-dir: 'doc/'
+          path-to-flake-dir: 'doc/'
+          branch: "update_flake_lock_doc"

.github/workflows/update-flake-lock-example.yaml

@@ -19,4 +19,5 @@ jobs:
           pr-title: "Update example/flake.lock"
           pr-labels: |
             automated
-          path-to-flake-dir: 'example/'
+          path-to-flake-dir: 'example/'
+          branch: "update_flake_lock_example"