gh-38521: Fix `sage_bootstrap.flock` for Python 3.13 (fedora-41)
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Seen on Fedora 41, which already ships Python 3.13:
https://github.com/mkoeppe/sage/actions/runs/10426436105/job/28893965205
#step:11:10930
```
#28 943.2 [pip-24.0] [spkg-pipinst] File
"/sage/build/bin/../sage_bootstrap/flock.py", line 15, in <module>
#28 943.2 [pip-24.0] [spkg-pipinst] import pipes
#28 943.2 [pip-24.0] [spkg-pipinst] ModuleNotFoundError: No module
named 'pipes'
```
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URL: https://github.com/sagemath/sage/pull/38521
Reported by: Matthias Köppe
Reviewer(s): François Bissey, Kwankyu Lee, Matthias Köppe
