Add mysql to PR build

Author: glucaci

.github/workflows/dotnet.yml

@@ -55,6 +55,22 @@ jobs:
         run: dotnet build --no-restore
       - name: MongoDB Tests
         run: dotnet test test/WorkflowCore.Tests.MongoDB --no-build --verbosity normal -p:ParallelizeTestCollections=false
+  MySQL-Tests:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - name: Setup .NET
+        uses: actions/setup-dotnet@v1
+        with:
+          dotnet-version: |
+            3.1.x
+            6.0.x
+      - name: Restore dependencies
+        run: dotnet restore
+      - name: Build
+        run: dotnet build --no-restore
+      - name: MySQL Tests
+        run: dotnet test test/WorkflowCore.Tests.MySQL --no-build --verbosity normal -p:ParallelizeTestCollections=false
   PostgreSQL-Tests:
     runs-on: ubuntu-latest
     steps: