Bump actions/checkout to v4 (#524)

Author: nickelc

.github/workflows/main.yml

@@ -15,7 +15,7 @@ jobs:
       matrix:
         version: [stable, beta, nightly]
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
 
       - name: Set toolchain
         run: |
@@ -48,7 +48,7 @@ jobs:
     name: MSRV
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
 
       - name: Install stable toolchain
         run: |
@@ -75,7 +75,7 @@ jobs:
     name: Lint
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
 
       - name: Install stable toolchain
         run: |