update all CI to use dotnet 5.0

Author: Heliozoa

.github/workflows/test.yml

@@ -40,7 +40,7 @@ jobs:
       - uses: actions/checkout@v2
       - uses: actions/setup-dotnet@v1
         with:
-          dotnet-version: "3.1.x"
+          dotnet-version: "5.0.x"
       - name: Diagnostics
         run: "gci env:"
       - name: Build test binary
@@ -54,7 +54,7 @@ jobs:
       - uses: actions/checkout@v2
       - uses: actions/setup-dotnet@v1
         with:
-          dotnet-version: "3.1.x"
+          dotnet-version: "5.0.x"
       - name: Build test binary
         run: cargo test --no-run --verbose
       - name: Run tests