Pin back pre-commit due to incompatibilities on windows

[Pasarus]

Description of work.
ad to pin back to 2.15 as we can't handle changes made here (pre-commit/pre-commit#2065 added in 2.16) on windows yet. Longer term we should change how we handle windows pre-commit, but we have no reason to put in the work yet.

To test:

• Create a fresh conda environment in windows
• Using a fresh clone of the mantid source configure cmake
• Change some code and try to commit these changes
• Pre-commit should run

There is no associated issue.

This does not require release notes because Not user facing

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Reviewer

Please comment on the following (full description):

Code Review

• Is the code of an acceptable quality?
• Does the code conform to the coding standards?
• Are the unit tests small and test the class in isolation?
• If there is GUI work does it follow the GUI standards?
• If there are changes in the release notes then do they describe the changes appropriately?
• Are the release notes saved in a separate file, using Issue or PR number for file name and in the correct location?

Functional Tests

• Do changes function as described? Add comments below that describe the tests performed?
• Do the changes handle unexpected situations, e.g. bad input?
• Has the relevant (user and developer) documentation been added/updated?

Does everything look good? Mark the review as Approve. A member of @mantidproject/gatekeepers will take care of it.

[thomashampson]

Fixes the problem. We'll have to consider this when moving all our version numbers to a single place.