Make sure we have mkcert

Author: rfay

.github/workflows/tests.yml

@@ -35,7 +35,7 @@ jobs:
     - uses: actions/checkout@v2
     - name: Environment setup
       run: |
-        brew install bats-core
+        brew install bats-core mkcert
         mkcert -install
 
     - name: Use ddev latest stable