Unreliable file locking

Gin file locking seems to not work reliably across setups as many users following ephy_testing_data contribution guideline unintentionally provide unlocked files despite executing the `gin lock *` prior to `gin upload`, see https://gin.g-node.org/NeuralEnsemble/ephy_testing_data/src/master/README.md and e.g. https://gin.g-node.org/NeuralEnsemble/ephy_testing_data/pulls/53

I failed to reproduce the issue on ubuntu with the following set of gin/git/git-annex versions:
```
GIN command line client 1.11 Build 001459 (103e923620de08ff77cf290e0b840a6d66cebfe1)
git: 2.30.0
git-annex: 8.20201129-geb388e6
```
and
```
GIN command line client 1.12 Build 001474 (b3e038038a6be25034de12f00b3fc10df26b785f)
git: 2.30.2
git-annex: 8.20210428-g571d146
```

Maybe this issue is related to the OS?