[Fix] jsx-key: detect conditional returns

[yialo]

Catch React key absence for conditional return without block statement:

const TestCase = () => {
  const list = [1, 2, 3, 4, 5];
  return (
    <div>
      {list.map(item => {
        if (item < 2) return <div>{item}</div>;
        else if (item < 5) return <div />;
        else return <div />;
      })}
    </div>
  );
};

[codecov]

Codecov Report

Merging #3630 (9acfec2) into master (422ff33) will increase coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head 9acfec2 differs from pull request most recent head ecadb92. Consider uploading reports for the commit ecadb92 to get more accurate results

@@           Coverage Diff           @@
##           master    #3630   +/-   ##
=======================================
  Coverage   97.64%   97.64%           
=======================================
  Files         132      132           
  Lines        9358     9360    +2     
  Branches     3425     3426    +1     
=======================================
+ Hits         9138     9140    +2     
  Misses        220      220           

Files Changed	Coverage Δ
lib/rules/jsx-key.js	99.16% <100.00%> (+0.01%)	⬆️

[ljharb]

Seems straightforward, thanks!