fix: typo (occured -> occurred) in machine_util comments

[SAY-5]

What this PR does / why we need it:
Fixes 'occured' -> 'occurred' typo in machine_util comments (docs/development/machine_error_codes.md and pkg/util/provider/machinecontroller/machine_util.go).

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:
String/comment-only change, no functional impact.

Release note:

NONE

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[SAY-5]

Pushed 8512ea9, folded #1101's docs/development/machine_error_codes.md fix into this branch and closed #1101.