fix: panic on webhook with nil body

[NickUfer]

Related issue(s)

Fixes #1885 by ensuring the body reader is never nil. See golang/go#32897

Checklist

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Further Comments

[aeneasr]

Nice find :)

Could you maybe also add a test case for this, to ensure there are no regressions?

[aeneasr]

Justin case you missed this:

Could you maybe also add a test case for this, to ensure there are no regressions?

:)

[NickUfer]

Hope this test is enough, didn't know how I should test the webhook execute function in any good way