For #13715, this:
- Upgrades the Go version to `1.21.1`, infrastructure changes are
addressed separately at https://github.com/fleetdm/fleet/pull/13878
- Upgrades the linter version, as the current version doesn't work well
after the Go upgrade
- Fixes new linting errors (we now get errors for memory aliasing in
loops! 🎉 )
After this is merged people will need to:
1. Update their Go version. I use `gvm` and I did it like:
```
$ gvm install go1.21.1
$ gvm use go1.21.1 --default
```
2. Update the local version of `golangci-lint`:
```
$ go install github.com/golangci/golangci-lint/cmd/golangci-lint@v1.54.2
```
3. (optional) depending on your setup, you might need to re-install some
packages, for example:
```
# goimports to automatically import libraries
$ go install golang.org/x/tools/cmd/goimports@latest
# gopls for the language server
$ go install golang.org/x/tools/gopls@latest
# etc...
```
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