github: force Go 1.16 or higher

Author: mmatczuk

.github/workflows/main.yml

@@ -17,6 +17,8 @@ jobs:
     steps:
       - uses: actions/checkout@v2
       - uses: actions/setup-go@v2
+        with:
+          go-version: '^1.16'
       - uses: actions/cache@v2
         id: gomod-cache
         with: