Upgrades Go version to 1.21.0 and updates GH actions to use go.mod instead of a hard-coded Go version. Also modifies golangCI to implement lint version updater.
Fixes #998
Quick checks:
[x] There is no other pull request for the same update/change.
[ ] I have written unit tests.
[x] I have made sure that the PR is of reasonable size and can be easily reviewed.
Description
Upgrades Go version to 1.21.0 and updates GH actions to use go.mod instead of a hard-coded Go version. Also modifies golangCI to implement lint version updater.
Fixes #998
Quick checks: