[CI] Updates actions/checkout to v7

Author: sanpii

.github/workflows/ci.yml

@@ -6,7 +6,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v7
       - uses: actions-rs/toolchain@v1
         with:
           toolchain: stable
@@ -22,7 +22,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v7
       - uses: actions-rs/toolchain@v1
         with:
           toolchain: stable
@@ -41,7 +41,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v7
       - uses: actions-rs/toolchain@v1
         with:
           toolchain: stable