Auto merge of rust-lang#9249 - JohnTitor:book-prefer-checkout-v3, r=flip1995

Use `action/checkout@v3` in the book

As this type of document is often copied/pasted, using a newer version of `actions/checkout` would be better.

changelog: none

Signed-off-by: Yuki Okushi <[email protected]>

Author: bors

book/src/continuous_integration/github_actions.md

@@ -15,7 +15,7 @@ jobs:
   clippy_check:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v1
+      - uses: actions/checkout@v3
       - name: Run Clippy
         run: cargo clippy --all-targets --all-features
 ```