Update x/tools and add go v1.21,v1.22 in CI workflows

[ryicoh]

In go v1.21, the test succeeds, but it fails in go v1.22.
The reason was that x/tools was outdated, so I updated it to the latest version.

I have:

• Added tests covering the bug / feature (see testing)
• Updated any relevant documentation (see docs)

[coveralls]

coverage: 75.869% (-0.08%) from 75.945%
when pulling 656d6fb on ryicoh:update-x-tools
into e174d59 on 99designs:master.

[StevenACoffman]

So something in Go 1.22 changed and it got much more pedantic.
The go generate ./... would hit the comment in main.go:

//go:generate go generate ./_examples/...

and give an error:

pattern ./_examples/...: directory prefix _examples does not contain main module or its selected dependencies

This was hard to see, as the old lint workflow did not echo commands and would run all of check-fmt, check-generate, check-coverage, golangci/golangci-lint-action.

The fix was to change the main.go generate comment to this:

//go:generate sh generate_examples.sh

and then in the script, I could do:

#!/bin/sh
cd _examples
go generate ./... || return 0

In GitHub actions, we don't really care much if it works for that directory, since we will immediately try again. The main.go comment is really only there to avoid having PRs from new contributors who would constantly stumble on forgetting to generate the _examples. Ideally, you would run go generate on _examples after the root.

I separated the action checks, added some debugging, and added dependabot so this is less likely to be so confusing in the future and we are more assertive about staying up to date with our dependencies.