docs: fix typo (succesful -> successful) in machine_error_codes

[SAY-5]

Minor typo fix in documentation.

[gardener-prow]

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[aaronfern]

Thanks for the PRs @SAY-5
I also see that you opened another PR #1100
Could you consolidate them both into one?

[SAY-5]

Sure — I'll fold #1100's typo fix into this PR and close the other one.

[SAY-5]

Consolidated into #1100 as requested — the doc fix is now commit 8512ea9 on the same branch.