Fix clock trigger execution retry delay bug

[MetRonnie]

Closes #5217

Fix bug where old-style clock triggered tasks would skip execution retry delays and just retry immediately.

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).
• No dependency changes
• Tests are included
• CHANGES.md entry included if this is a change that can affect users
• No docs needed

[oliver-sanders]

I think this is left behind from an old configuration we removed at Cylc 8?

[wxtim]

according to the Cylc 7 code these were obseleted at 7.2.2

[hjoliver]

I see you've now removed __slots__ declarations from the Interval subclasses. Python docs seems to say this means instances will get an attributes dict as well:

The action of a slots declaration is not limited to the class where it is defined. slots declared in parents are available in child classes. However, child subclasses will get a dict and weakref unless they also define slots (which should only contain names of any additional slots).

I guess that means subclasses with no additional attributes should declare an empty slots tuple?

[oliver-sanders]

Could you bump __slots__ fiddling / tidying to another PR to make it easier to get this in for 8.1.0 as the actual fix is only two lines?

[MetRonnie]

Done

[oliver-sanders]

LGTM.

Should try to get rid of the sleep in the test as sleeps are a major cause of test flakyness. If the sleep is functional the test could be run in no-detach mode to avoid the issue.

[MetRonnie]

Got rid of the sleep in the test

[MetRonnie]

[oliver-sanders]

They are apparently looking into the upload failure issue.

[wxtim]

I'll be happy to merge once the tests have passed.