actually run the mysql tests

Author: jbr

.github/workflows/ci.yaml

@@ -82,6 +82,12 @@ jobs:
         command: test
         args: --all --features sqlite,async_std
 
+    - name: mysql tests
+      uses: actions-rs/cargo@v1
+      with:
+        command: test
+        args: --all --features mysql,async_std -- --test-threads=1
+
   check_fmt_and_docs:
     name: Checking fmt, clippy, and docs
     runs-on: ubuntu-latest