logging: update header timestamp on rollover

[oliver-sanders]

When the scheduler log rolls over, the header lines get logged with the original timestamp rather than the rollover time which is a tad confusing.

Test using:

# global.cylc

[scheduler]
  [[logging]]
    maximum size in bytes = 200

Check List

• I have read CONTRIBUTING.md and added my name as a Code Contributor.
• Contains logically grouped changes (else tidy your branch by rebase).
• Does not contain off-topic changes (use other PRs for other changes).
• Applied any dependency changes to both setup.cfg (and conda-environment.yml if present).
• Tests are included (or explain why tests are not needed).
• Changelog entry included if this is a change that can affect users
• Cylc-Doc pull request opened if required at cylc/cylc-doc/pull/XXXX.
• If this is a bug fix, PR should be raised against the relevant ?.?.x branch.

[wxtim]

IMO it's entirely reasonable not to test assigning the output of a standard library function, and marking this as not needing testing gives us a better idea of what is and isn't tested.

Suggested change

	now = time()
	now = time() # pragma: no cover

I'm now questioning whether Cov should even pick this up.

[oliver-sanders]

I'm confused, codecode says this is covered:

codecov/patch — 100.00% of diff hit (target 97.00%)

[wxtim]

[oliver-sanders]

[wxtim]

Whatev. Not super important. Wierd though. I think that you can merge this on one review if you want.

[wxtim]

• Read code.
• Manually tested.

Doesn't have a unit test, but perhaps the game isn't worth the candle for this change.