ci: bump actions/checkout from 4 to 6 for kdf (#2199)

Author: dependabot[bot]

.github/workflows/kdf.yml

@@ -28,7 +28,7 @@ jobs:
           - thumbv7em-none-eabi
           - wasm32-unknown-unknown
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - uses: RustCrypto/actions/cargo-cache@master
       - uses: dtolnay/rust-toolchain@master
         with:
@@ -44,7 +44,7 @@ jobs:
           - 1.85.0 # MSRV
           - stable
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - uses: RustCrypto/actions/cargo-cache@master
       - uses: dtolnay/rust-toolchain@master
         with: