Update actions/checkout in GitHub Actions workflows to v3

.github/workflows/macos.yml

@@ -14,7 +14,7 @@ jobs:
 
     name: "${{matrix.config.os}}"
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v3
 
     - name: Build Release
       run: |

.github/workflows/ubuntu.yml

@@ -23,7 +23,7 @@ jobs:
 
     name: "${{matrix.compiler.cc}}"
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v3
 
     - name: Configure clang
       run: |

.github/workflows/windows.yml

@@ -14,7 +14,7 @@ jobs:
 
     name: "${{matrix.config.vs}}"
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v3
 
     - name: Build Win32
       shell: bash