use consisitent actions/checkout version

Author: burner1024

.github/workflows/build.yml

@@ -10,7 +10,7 @@ jobs:
         uses: actions/checkout@v2
 
       - name: Checkout Detours
-        uses: actions/checkout@master
+        uses: actions/checkout@v2
         with:
           repository: microsoft/Detours
           ref: '4.0.1'

.github/workflows/release.yml

@@ -26,7 +26,7 @@ jobs:
             ${{ runner.os }}-
 
       - name: Checkout Detours
-        uses: actions/checkout@master
+        uses: actions/checkout@v2
         with:
           repository: microsoft/Detours
           ref: '4.0.1'