Update to `go1.21`

[timvaillancourt]

Description

This PR updates the builds from go1.17->go1.21 (current stable). Also:

• the golang docker images are based on bullseye instead of stretch
• the golangci-lint version was updated to v1.54.2 to support go1.21
  • Some files were updated to remove new linter complaints for deprecated io/ioutil
• ran go mod tidy and go mod vendor

Finally, GitHub Actions were updated to ubuntu-latest, except the replica tests which had problems with MySQL 5.7 and linked libraries - I'm working on a new PR to fix this

In case this PR introduced Go code changes:

• [x] contributed code is using same conventions as original code
• [x] script/cibuild returns with no formatting errors, build errors or unit test errors.

[meiji163]

Because of GitHub's "hack" to upload gh-ost binaries internally, we have to change "stretch" to "bullseye" in this line https://github.com/github/gh-ost/blob/679d39e5ce45c55415e656bd9de3c1137b34bf55/script/build-deploy-tarball#L34

[timvaillancourt]

Because of GitHub's "hack" to upload gh-ost binaries internally, we have to change "stretch" to "bullseye" in this line

https://github.com/github/gh-ost/blob/679d39e5ce45c55415e656bd9de3c1137b34bf55/script/build-deploy-tarball#L34

@meiji163 makes sense. Updated 👍