ci: Update to actions/checkout@v4.

Author: waywardmonkeys

.github/workflows/ci.yaml

@@ -20,7 +20,7 @@ jobs:
           nightly
         ]
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: dtolnay/rust-toolchain@master
         with:
           toolchain: ${{ matrix.rust }}
@@ -32,7 +32,7 @@ jobs:
     name: No Std (stable)
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: dtolnay/rust-toolchain@stable
         with:
           target: thumbv6m-none-eabi
@@ -43,7 +43,7 @@ jobs:
     name: No Std (1.31.0)
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: dtolnay/rust-toolchain@1.31.0
         with:
           target: thumbv6m-none-eabi
@@ -53,7 +53,7 @@ jobs:
     name: Format
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: dtolnay/rust-toolchain@1.62.0
         with:
           components: rustfmt

.github/workflows/master.yaml

@@ -15,7 +15,7 @@ jobs:
       matrix:
         rust: [1.31.0, stable]
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: dtolnay/rust-toolchain@master
         with:
           toolchain: ${{ matrix.rust }}

.github/workflows/pr.yaml

@@ -11,7 +11,7 @@ jobs:
       matrix:
         rust: [1.31.0, stable]
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: dtolnay/rust-toolchain@master
         with:
           toolchain: ${{ matrix.rust }}
@@ -22,7 +22,7 @@ jobs:
     name: Format
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: dtolnay/rust-toolchain@1.62.0
         with:
           components: rustfmt