gha: update go versions to 1.19, 1.20

Note that go1.13 has reached EOL a long time ago; removing that version,
as packages are no longer compatible with it:

    go get github.com/philhofer/fwd
    # golang.org/x/tools/internal/gocommand
    Error: ../../../go/src/golang.org/x/tools/internal/gocommand/invoke.go:399:62: undefined: os.ErrProcessDone
    Error: Process completed with exit code 2.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

Author: thaJeztah

.github/workflows/ci.yaml

@@ -14,7 +14,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu, macos, windows]
-        golang: ['1.13', '1.16', '1.17']
+        golang: ['1.19', '1.20']
         # currently, we cannot run non-x86_64 machines on GitHub Actions cloud env.
     runs-on: ${{ matrix.os }}-latest
     name: CI golang ${{ matrix.golang }} on ${{ matrix.os }}