install dotnet in CI

Author: Heliozoa

.github/workflows/test.yml

@@ -21,6 +21,9 @@ jobs:
       - uses: r-lib/actions/setup-r@v1
         with:
           r-version: "3.5.3"
+      - uses: actions/setup-dotnet@v1
+        with:
+          dotnet-version: "3.1.x"
       - name: Install tmc-r-tester
         run: |
           Rscript -e 'install.packages(c("devtools","testthat", "httr", "curl"),repos="https://ftp.eenet.ee/pub/cran/")'
@@ -34,6 +37,9 @@ jobs:
     runs-on: windows-latest
     steps: # TODO: install missing dependencies and run all tests on windows
       - uses: actions/checkout@v2
+      - uses: actions/setup-dotnet@v1
+        with:
+          dotnet-version: "3.1.x"
       - name: Build test binary
         run: cargo test --no-run --verbose
       - name: Run tests
@@ -43,6 +49,9 @@ jobs:
     runs-on: macos-latest
     steps: # TODO: install missing dependencies and run all tests on macos
       - uses: actions/checkout@v2
+      - uses: actions/setup-dotnet@v1
+        with:
+          dotnet-version: "3.1.x"
       - name: Build test binary
         run: cargo test --no-run --verbose
       - name: Run tests