fix: 'ocis backup consistency' file regex

'ocis backup consistency' was stumbling over revision (and trash) nodes
whose timestamp lacked the nanosecond component (which happens if the nanoseconds
of the mtime are 0)

Fixes: #9498
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Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f