Fix escaping in RegExp.prototype.source

[raskad]

This PR fixes the line terminator escaping in RegExp.prototype.source.

[github-actions]

Test262 conformance changes

Test result	main count	PR count	difference
Total	95,960	95,960	0
Passed	76,594	76,596	+2
Ignored	18,477	18,477	0
Failed	889	887	-2
Panics	0	0	0
Conformance	79.82%	79.82%	+0.00%

Fixed tests (2):

test/built-ins/RegExp/prototype/source/value-line-terminator.js [strict mode] (previously Failed)
test/built-ins/RegExp/prototype/source/value-line-terminator.js (previously Failed)

[codecov]

Codecov Report

Attention: 4 lines in your changes are missing coverage. Please review.

Comparison is base (6be4296) 47.46% compared to head (97cd840) 47.46%.

Files	Patch %	Lines
core/engine/src/builtins/regexp/mod.rs	0.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3619      +/-   ##
==========================================
- Coverage   47.46%   47.46%   -0.01%     
==========================================
  Files         475      475              
  Lines       46044    46046       +2     
==========================================
  Hits        21855    21855              
- Misses      24189    24191       +2     

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[jedel1043]

Nice catch!

[HalidOdat]

Looks good to me! :)