Bump actions/checkout from 6.0.2 to 7.0.0 in the github-actions group

Closes https://github.com/dart-lang/flute/pull/32

GitOrigin-RevId: e0ad46b832e7c7b177a681779194106b69514fa9
Change-Id: I60517b004ae90a010827f67223d082c0f50b56b3
Reviewed-on: https://dart-review.googlesource.com/c/flute/+/519082
Commit-Queue: Alexander Thomas <athom@google.com>
Reviewed-by: Alexander Thomas <athom@google.com>

.github/workflows/ci.yaml

diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
index f1d00cc..e66104c 100644
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -20,7 +20,7 @@
           echo "Running on ${{ runner.os }}"
           echo "Branch: ${{ github.ref }}; repo: ${{ github.repository }}."
       - name: Fetch sources
-        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd
+        uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0
       - name: Install Dart SDK
         uses: dart-lang/setup-dart@65eb853c7ba17dde3be364c3d2858773e7144260
         with: