account for optional Z in time strs

[sappelhoff]

PR Description

fix a problem that was reported here: https://mne.discourse.group/t/how-to-import-fnirs-data-from-a-local-dataset/8481/3?u=sappelhoff

cc @hoechenberger

Merge checklist

Maintainer, please confirm the following before merging. If applicable:

• [ ] All comments are resolved
• [ ] This is not your own PR
• [ ] All CIs are happy
• [ ] PR title starts with [MRG]
• [ ] whats_new.rst is updated
• [ ] New contributors have been added to CITATION.cff
• [ ] PR description includes phrase "closes <#issue-number>"

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 97.60%. Comparing base (87eea28) to head (8566784). Report is 15 commits behind head on main.

:exclamation: Current head 8566784 differs from pull request most recent head f907308. Consider uploading reports for the commit f907308 to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1240 +/- ## ========================================== - Coverage 97.61% 97.60% -0.02% ========================================== Files 40 40 Lines 8685 8682 -3 ========================================== - Hits 8478 8474 -4 - Misses 207 208 +1 ```

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[hoechenberger]

@sappelhoff I tried to give it a shot

Code isn't super pretty but I think the logical flow is very clear

Didn't run or write any tests yet

[hoechenberger]

I added some tests

[sappelhoff]

Very kind of you to include me in the commit changelog message 🤣

Thanks, I think this is much saner behavior now!!

[hoechenberger]

Very kind of you to include me in the ~commit~ changelog message 🤣

yeah now worries, you started the PR after all :)

Thanks, I think this is much saner behavior now!!

let's hope I / we didn't overlook something here … but I think in any case, we're behaving more correctly now than before!