Update github workflows to actions/checkout@v3

Author: jannic

.github/workflows/clippy.yml

@@ -8,7 +8,7 @@ jobs:
   clippy:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - uses: dtolnay/rust-toolchain@master
         with:
           # embedded-hal-async needs nightly.

.github/workflows/rustfmt.yml

@@ -9,7 +9,7 @@ jobs:
   fmt:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - uses: dtolnay/rust-toolchain@master
         with:
           toolchain: nightly

.github/workflows/test.yml

@@ -26,7 +26,7 @@ jobs:
           - thumbv7m-none-eabi
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - uses: dtolnay/rust-toolchain@master
         with:
           toolchain: ${{ matrix.rust }}