ci: extend GOPROXY list

[kamilsk]

I just added https://gocenter.io as a reserve proxy because https://proxy.golang.org may not be available.

Any comments are welcome.

refs #1155

[kamilsk]

default GOPROXY value is

$ go env GOPROXY
https://proxy.golang.org,direct

[codecov-io]

Codecov Report

Merging #1158 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1158   +/-   ##
=======================================
  Coverage   82.98%   82.98%           
=======================================
  Files          58       58           
  Lines        3262     3262           
=======================================
  Hits         2707     2707           
  Misses        473      473           
  Partials       82       82

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[github-actions]

This pull request has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.