Fixes issues with update_all, increment, and decrement

[serch]

This upstream PR citusdata#223 broke some usages of update_all. Both increment and decrement use update_all.

For example a call to model.decrement!(:counter) generates an UPDATE query with SET "counter" = NULL instead of the correct SET "counter" = COALESCE("counter", 0).

The bug was noticed 7 months after the PR that introduced it was created

https://github.com/citusdata/activerecord-multi-tenant/pull/223/files#r1743665204

the author of the above comment Laykou and another user Amit909Singh discussed the issue (all comments can be seen in the PR citusdata#223) and Amit909Singh mentioned they fixed it in citusdata#223 (comment)

I cherry-picked his commit Amit909Singh@c08b636

and

• removed rails and activerecord 6.0 and 6.1 from the test suite (tests were failing)
• added ruby 3.4, rails 8.1, and activerecord 8.1 to the github actions workflow
• added instructions on how to run the tests locally and brought back the appraisal gemfiles
• added tests for increment and decrement
• fixed warnings in the docker-compose file

I also submitted a PR upstream, but the gem is abandoned so I doubt it will ever get merged.
citusdata#282