Add git-blame-ignore-revs file

Add git-blame-ignore-revs file

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### Description

This is helpful when using git-blame on files that 'black' heavily modified back in 2019'ish. While git doesn't specify this name, there seems to be a general convention around using this. See Django [1] and Twisted [2], for example.

[1] https://github.com/django/django/blob/main/.git-blame-ignore-revs
[2] https://github.com/twisted/twisted/blob/trunk/.git-blame-ignore-revs

### Checklist
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This pull request is:

- [ ] A documentation / typographical error fix
	- Good to go, no issue or tests are needed
- [ ] A short code fix
	- please include the issue number, and create an issue if none exists, which
	  must include a complete example of the issue.  one line code fixes without an
	  issue and demonstration will not be accepted.
	- Please include: `Fixes: #<issue number>` in the commit message
	- please include tests.   one line code fixes without tests will not be accepted.
- [ ] A new feature implementation
	- please include the issue number, and create an issue if none exists, which must
	  include a complete example of how the feature would look.
	- Please include: `Fixes: #<issue number>` in the commit message
	- please include tests.
- [x] None of the above
	- This is infra-related

**Have a nice day!**

Closes: #7964
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/7964
Pull-request-sha: 4be7330a51ee48e360e10a7c5a6d90fea62a9515

Change-Id: I49863f629a64a5320d9d851d1220400fb45dead9