test with latest go version (#150)

Signed-off-by: Bob Callaway <bcallaway@google.com>

Author: bobcallaway

.github/workflows/test-action.yml

@@ -206,8 +206,8 @@ jobs:
           - ubuntu-latest
           - windows-latest
         go_version:
-          - '1.19'
           - '1.20'
+          - '1.21'
     name: Try to install cosign with go ${{ matrix.go_version }}
     steps:
       - uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4.1.1