📖Remove latest from setupenvtest docs

[troy0820]

Instead of saying use latest which can have a different go version in the go.mod at the time of reading the doc, we can just use the last release.

If people want to install at latest, they will do so at their own will.

Fixes #3358

/assign @sbueringer
/assign @alvaroaleman

Not sure if this is sufficient but it does document this a little better than before.

[alvaroaleman]

Maybe it would be better to instead tell ppl to download it from a github release to avoid keeping this up to date? We will most likely forget to do that

[sbueringer]

Let's point to the GitHub release first and then mention this with release-major.minor or some other placeholder

[k8s-ci-robot]

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[sbueringer]

/lgtm

I'm fine with mentioning a release branch. I would see this only as an example that we don't have to keep up to date

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: 4b0c3f2b4caeb362683d4aa5ab77b4fb72e916f6