chore: use u flag for regexes

[Biki-das]

Usage of the u flag with regular expressions is recommended.

The u flag has two effects:

It enables correct handling of UTF-16 surrogate pairs.
It ensures the correct behavior of regex character ranges.

/^[👍]$/.test("👍") //→ false
/^[👍]$/u.test("👍") //→ true

Make the regular expression throwing syntax errors early as disabling JavaScript specification Annex B[1] extensions.

Because of historical reason, JavaScript regular expressions are tolerant of syntax errors. For example, /\w{1, 2/ is a syntax error, but JavaScript doesn't throw the error. It matches strings such as "a{1, 2" instead. Such a recovering logic is defined in Annex B of Javascript specification.

The u flag disables the recovering logic Annex B of the Javascript specification. As a result, you can find errors early. This is similar to the strict mode.

[codecov-commenter]

Codecov Report

Merging #12249 (7031c68) into main (4f4be57) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main   #12249   +/-   ##
=======================================
  Coverage   67.52%   67.52%           
=======================================
  Files         328      328           
  Lines       17244    17244           
  Branches     5069     5069           
=======================================
  Hits        11644    11644           
  Misses       5567     5567           
  Partials       33       33           

Impacted Files	Coverage Δ
packages/jest-reporters/src/utils.ts	81.25% <100.00%> (ø)

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[SimenB]

cool, thanks!

[github-actions]

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