github/workflow: upgrade go-version to 1.16.x

Author: zchee

.github/workflows/benchmark.yml

@@ -17,10 +17,9 @@ jobs:
     strategy:
       matrix:
         os:
-          # https://github.com/actions/virtual-environments/blob/ubuntu20/20201210.0/images/linux/Ubuntu2004-README.md
-          - ubuntu-20.04
+          - ubuntu-20.04  # https://github.com/actions/virtual-environments/blob/main/images/linux/Ubuntu2004-README.md
         go-version:
-          - 1.15.x
+          - 1.16.x
     runs-on: ${{ matrix.os }}
 
     steps: