Cylc-flow: Remove executable bit of Python source code

[kinow]

Describe the bug

If you look at the Python source code under cylc, you will find some files that have the executable bit turned on. e.g. cylc.flow.scheduler_cli, cylc.flow.prerequisite, etc

I see no reason for having the files under cylc with +x.

Release version(s) and/or repository branch(es) affected?

master, 8.0a1

Steps to reproduce the bug

NA

Expected behavior

Source code simply with rw permissions.

Screenshots

Added in previous section.

Additional context

Pull requests welcome!
This is an Open Source project - please consider contributing a bug fix
yourself (please read CONTRIBUTING.md before starting any work though).

[kinow]

I never submitted a PR like this, but I think it should work. Something like chmod -x $file..., then commit the file, and prepare the PR.

[matthewrmshin]

Doh!

[hjoliver]

(It probably results from running primitive built-in unit tests during development, before we had proper unit tests).

[matthewrmshin]

Closed by #3385.