fix assorted oddities found by golangci-lint

[xrstf]

This PR fixes a lot of the errors found by various linters in golangci-lint, mostly focussing on

• errorlint, ensuring errors are not compared with == or type assertions anymore, but errors.Is() and errors.As() are used.
• strings.Replace(_, _, _, -1) == strings.ReplaceAll(_, _, _)
• string(buf.Bytes()) == buf.String()
• if strings.HasSuffix(a, b) { trim suffix } == strings.TrimSuffix()
• reqParam and warnings in the unit tests were entirely unused.
• I made the unit tests robust against people like me who trim spaces when saving a file. Previously some of the variables in the registry_test.go required trailing spaces in the Go code.

[kakkoyun]

Why are we removing these? Are they not used? Maybe there's something needs to be fixed in these tests.

[xrstf]

They are entirely unused, just like warnings was. It seemed there were other mechanisms in place to construct the request params (using the do field in each testcase)

[xrstf]

But I was also surprised that this amount of dead code would be here, so maybe the linter and me misinterpreted something? :)

[kakkoyun]

We might have changed the comparison method or something similar without realizing their intended use. Let's make sure if we can actually use them. Otherwise, happy to accept clean-ups.

[xrstf]

So from what I can see, the apiTest structure was introduced via #165 (released in v0.8.0). However I could not find a single revision in this repo that actually used the reqParam field.

[kakkoyun]

That's an ancient PR 😅 Thanks for digging it up. Then I'm ok with the changes. If anything becomes broken, we can fix them on consecutive PRs.

[kakkoyun]

@xrstf One last could you please let me know which linters have you used for these changes? It would be even better if you update the .golangci.yaml file with them so that we can preserve consistency for subsequent changes.

[xrstf]

No problemo. I first only fixed the low hanging fruit, as I did not intend for the linters to be enabled permanently. But if you want, gladly, we can make them permanent. I pushed a commit to enable them and fix the remaining not-so-low-hanging fruit. :)

[xrstf]

Not super sure about the Github action failing, I have the exact same golangci-lint version locally and it finishes without issues.

[kakkoyun]

@xrstf Could you, please rebase this one?
We merged #1056. I wonder how this looks after that one merged.

[xrstf]

@kakkoyun Can do :)

[kakkoyun]

@xrstf Do you think you can check this out this week? We want to cut a release.

[xrstf]

I can!

In the meaintime there was #1047, but I still assume that since the reqParams are unused, I can still remove them in this PR?

[xrstf]

Are the test failures are flakes? Locally make test seems to work just fine.

[kakkoyun]

Are the test failures are flakes? Locally make test seems to work just fine.

It seems like it :) Now, it is fixed.