Upgrade actions/checkout to v4

Author: JohnTitor

.github/workflows/autofix.yml

@@ -13,7 +13,7 @@ jobs:
       RUST_LIB_BACKTRACE: 1
 
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
         with:
           fetch-depth: 0
 

.github/workflows/labeler.yml

@@ -11,7 +11,7 @@ jobs:
     if: github.repository == 'rust-lang/glacier'
 
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
 
       - name: Build
         uses: ./.github/actions/build

.github/workflows/main.yml

@@ -7,7 +7,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
 
       - name: tab character check
         run: if grep -P '\t' -rn --color ices fixed; then exit 1; fi