gha: update go versions

[thaJeztah]

Looks like CI was no longer working, because ltag now required a newer version of go;

pushd $(mktemp -d) \
  && go get -u github.com/kunalkushwaha/ltag \
  && popd \
  && ./scripts/validate/fileheader
  shell: /usr/bin/bash -e {0}
  env:
    GOROOT: /opt/hostedtoolcache/go/1.13.15/x64
/tmp/tmp.wrQsimdF1t ~/work/spdystream/spdystream
# github.com/kunalkushwaha/ltag
Error: /home/runner/go/src/github.com/kunalkushwaha/ltag/bash.go:25:15: undefined: os.ReadFile
Error: /home/runner/go/src/github.com/kunalkushwaha/ltag/dockerfile.go:23:15: undefined: os.ReadFile
Error: /home/runner/go/src/github.com/kunalkushwaha/ltag/golang.go:23:15: undefined: os.ReadFile
Error: /home/runner/go/src/github.com/kunalkushwaha/ltag/makefile.go:15:15: undefined: os.ReadFile
Error: Process completed with exit code 2.

[thaJeztah]

@dims PTAL

[dims]

LGTM

[thaJeztah]

Thx! Let me get this one in, and rebase the other one 👍