fix(eslint-plugin): always ignore assignments in no-unnecessary-type-assertion

[JoshuaKGoldberg]

Fixes #3187.

Since TypeScript is smart about inferring types for variable assignments, I think it's reasonable to always exclude the right-hand-side of assignment expressions.

[typescript-eslint]

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[codecov]

Codecov Report

Merging #3235 (db0e026) into master (5414bf2) will decrease coverage by 0.13%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #3235      +/-   ##
==========================================
- Coverage   92.93%   92.80%   -0.14%     
==========================================
  Files         316      318       +2     
  Lines       10851    10974     +123     
  Branches     3067     3102      +35     
==========================================
+ Hits        10084    10184     +100     
- Misses        342      350       +8     
- Partials      425      440      +15     

Flag	Coverage Δ
unittest	92.80% <100.00%> (-0.14%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...-plugin/src/rules/no-unnecessary-type-assertion.ts	93.58% <100.00%> (-1.08%)	⬇️
packages/eslint-plugin/src/rules/no-unsafe-call.ts	95.23% <0.00%> (-4.77%)	⬇️
...eslint-plugin/src/rules/no-unsafe-member-access.ts	97.82% <0.00%> (-2.18%)	⬇️
...ckages/eslint-plugin/src/rules/no-unsafe-return.ts	98.24% <0.00%> (-1.76%)	⬇️
packages/eslint-plugin/src/util/types.ts	81.86% <0.00%> (-1.65%)	⬇️
...es/eslint-plugin/src/rules/no-unsafe-assignment.ts	92.96% <0.00%> (-0.26%)	⬇️
packages/eslint-plugin/src/rules/no-type-alias.ts	100.00% <0.00%> (ø)
...ages/eslint-plugin/src/rules/no-unsafe-argument.ts	81.15% <0.00%> (ø)
...ckages/eslint-plugin/src/util/getThisExpression.ts	84.61% <0.00%> (ø)

[bradzacher]

Yeah the change didn't consider all of the cases and was ultimately a bad one.

Thanks! One comment

[bradzacher]

THANKS!