Bump actions/checkout from 4 to 6 (#4380)

Bumps [actions/checkout](https://github.com/actions/checkout) from 4 to 6.

- vLLM main:
2918c1b49c

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.github/workflows/release_whl.yml

@@ -52,7 +52,7 @@ jobs:
          ) }}
     runs-on: ${{ matrix.os }}
     steps:
-    - uses: actions/checkout@ff7abcd0c3c05ccf6adc123a8cd1fd4fb30fb493 # v4.2.2
+    - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4.2.2
 
     - name: Print
       run: |