bump the minimum Go version to 1.16

Fedora 34 ships 1.16
RHEL 8.5 also ships 1.16

Signed-off-by: Ondřej Budai <ondrej@budai.cz>

.github/workflows/tests.yml

@@ -16,10 +16,10 @@ jobs:
     runs-on: ubuntu-20.04
     steps:
 
-      - name: Set up Go 1.15
+      - name: Set up Go 1.16
         uses: actions/setup-go@v2.1.5
         with:
-          go-version: 1.15
+          go-version: 1.16
         id: go
 
       - name: Check out code into the Go module directory