Update workflows to actions/checkout@v3

Author: dtolnay

.github/workflows/ci.yml

@@ -17,7 +17,7 @@ jobs:
       matrix:
         rust: [nightly, beta, stable, 1.59.0]
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - uses: dtolnay/rust-toolchain@master
         with:
           toolchain: ${{matrix.rust}}
@@ -29,7 +29,7 @@ jobs:
     runs-on: ubuntu-latest
     if: github.event_name != 'pull_request'
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - uses: dtolnay/rust-toolchain@clippy
       - run: cargo clippy -- -Dclippy::all -Dclippy::pedantic
 
@@ -38,6 +38,6 @@ jobs:
     runs-on: ubuntu-latest
     if: github.event_name != 'pull_request'
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - uses: dtolnay/install@cargo-outdated
       - run: cargo outdated --exit-code 1