cylc clean: fix bug where --rm share would not clean share/cycle symlink first

[MetRonnie]

Fixes a bug possibly (?) seen before by some users at the Met Office, but not tracked by an issue.

If share/cycle is a symlink directory, it must also be cleaned first when only specifying --rm share.

Reproduceable example

# global.cylc
[install]
    [[symlink dirs]]
        [[[localhost]]]
            share = $HOME/sym-other
            share/cycle = $HOME/sym-cycle

$ cylc play <workflow>
$ cylc stop <workflow>
$ cylc clean <workflow> --rm share
# Restart:
$ cylc play <workflow>
WorkflowFilesError: Symlink dir target already exists: (~/cylc-run/<workflow>/share/cycle ->) ~/sym-cycle/cylc-run/<workflow>/share/cycle
Tip: in future, use 'cylc clean' instead of manually deleting workflow run dirs.

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
• Changelog entry included if this is a change that can affect users
• No docs needed
• If this is a bug fix, PR should be raised against the relevant ?.?.x branch.

[oliver-sanders]

Fixes a bug possibly (?) seen before by some users at the Met Office, but not tracked by an issue.

If it only applies to the --rm option, then I don't think this has been reported. There was an unconfirmed report of cylc clean (no opts) leaving files behind, however, the evidence was destroyed so it couldn't be verified.

[oliver-sanders]

$ cylc play
WorkflowFilesError: Symlink dir target already exists: (~/cylc-run//share/cycle ->) ~/sym-cycle/cylc-run//share/cycle
Tip: in future, use 'cylc clean' instead of manually deleting workflow run dirs.

I actually don't get this traceback, however, I can confirm the share/cycle directory was left behind before but isn't after.

[MetRonnie]

@oliver-sanders RE: the traceback you were getting, can you try this in your testing?

Suggested change

	if any(is_relative_to(symlink_dir, path) for path in matches):
	if (
	any(is_relative_to(symlink_dir, path) for path in matches)
	and symlink_dir.is_symlink()
	):

[oliver-sanders]

Seems to do the trick!