Add cargo-semver-checks to CI to ensure semver compliance

[Christoph-AK]

In the past we struggled with SemVer compliance (See #140, #169, #200, #246).

Today I read about cargo-semver-checks (also see the article on Predrags blog.)

Seems like it should be as simple as running the github action. We might want to run it on every tag, and tag all new versions according to the version in the Cargo.toml.

This doesn't entirely fix the problem, but should improve this going forward, especially as there are probably more SemVer-lints coming to the crate.

Might also want to enable http-registry in it once it lands.

[github-actions]

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[Christoph-AK]

I still want this. I would work on this if I find the time (if noone did it before, should be a really easy integration), so please leave this open for the time being.