test_timer can fail for no real reason under certain conditions

[ri0t]

Helloes,

under certain conditions (maybe system load being high?) the timer tests can fail randomly:

error: builder for '/nix/store/r19bvjb3xkabyzl3w2s19kw16gafachy-python3.11-devtools-0.12.2.drv' failed with exit code 1;
last 10 log lines:
> E - 3 times: mean=0.00Xs stdev=0.00Xs min=0.00Xs max=0.00Xs
> E ? -
> E + 3 times: mean=0.00Xs stdev=0.00Xs min=0.00Xs max=0.010s
> E ? +
>
> tests/test_timer.py:31: AssertionError
> =========================== short test summary info ============================
> FAILED tests/test_timer.py::test_multiple - AssertionError: assert '0.00X: 0.010... max=0.010s\n' == '0.00X: 0.00X... m...
> ============ 1 failed, 95 passed, 8 skipped, 6 deselected in 0.58s =============

Notice the minor timer invariance of 0.010s. I restarted the whole build process a few times and suddenly it built without any changes.

[samuelcolvin]

Well probably because of unexpected low system resources causing the slower execution.

PR welcome to fix this.