main.yml: Update actions/checkout to be v3

.github/workflows/main.yml

@@ -25,7 +25,7 @@ jobs:
         CC: ["gcc", "clang"]
         TLS: ["no", "openssl", "gnutls", "mbedtls"]
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - name: setup
         run: |
           sudo apt-get update && sudo apt-get install -y libcunit1-dev libmbedtls-dev libgnutls28-dev libtool libtool-bin exuberant-ctags valgrind
@@ -53,7 +53,7 @@ jobs:
   tinydtls-build:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
         with:
           submodules: recursive
       - name: setup
@@ -75,7 +75,7 @@ jobs:
       matrix:
         TLS: ["no", "openssl", "gnutls", "mbedtls", "tinydtls"]
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
         with:
           submodules: recursive
       - name: setup
@@ -118,7 +118,7 @@ jobs:
       matrix:
         OS: ["contiki", "lwip"]
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - name: setup
         run: |
           ./autogen.sh
@@ -132,7 +132,7 @@ jobs:
     runs-on: windows-latest
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
 
       - name: Add MSBuild to PATH
         uses: microsoft/setup-msbuild@v1
@@ -170,7 +170,7 @@ jobs:
   additional-tests:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
         with:
           submodules: recursive
       - name: setup
@@ -186,7 +186,7 @@ jobs:
   documentation:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
         with:
           submodules: recursive
       - name: setup
@@ -210,7 +210,7 @@ jobs:
   distribution:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
         with:
           submodules: recursive
       - name: setup