dev: Remove Ruff test path ignores and fix errors

[ajay-sentry]

Purpose/Motivation

Part of the lint enhancement epic, this PR brings shared's ruff.toml to parity with codecov-api's here: https://github.com/codecov/codecov-api/blob/d37f5c7b077fa745e07c2b82666f305dae33b631/ruff.toml#L38-L42

The main change with this PR is to just remove the "ignore" path I set previously for all test files. In hindsight, I shouldn't have done this to begin with since we still want all of ruff's formatting and import deletion etc. etc for test files.

In the process I've also gone and fixed a lot of the rules for unused vars, or == None vs. is None, and a couple of list comprehension updates from the PERF rules.

Links to relevant tickets

Closes codecov/engineering-team#2052

What does this PR do?

This PR adds the rules listed above and fixes any errors that stemmed from them.

Legal Boilerplate

Look, I get it. The entity doing business as "Sentry" was incorporated in the State of Delaware in 2015 as Functional Software, Inc. In 2022 this entity acquired Codecov and as result Sentry is going to need some rights from me in order to utilize my contributions in this PR. So here's the deal: I retain all rights, title and interest in and to my contributions, and by keeping this boilerplate intact I confirm that Sentry can use, modify, copy, and redistribute my contributions, under Sentry's choice of terms.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.25%. Comparing base (de9dc30) to head (465d0eb).

❗ Current head 465d0eb differs from pull request most recent head f7edcf3

Please upload reports for the commit f7edcf3 to get more accurate results.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #281      +/-   ##
==========================================
- Coverage   89.86%   89.25%   -0.62%     
==========================================
  Files         358      324      -34     
  Lines       11437     9992    -1445     
  Branches     2050     1783     -267     
==========================================
- Hits        10278     8918    -1360     
+ Misses       1074     1004      -70     
+ Partials       85       70      -15     

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