bug: NativeFunctionTypeDeclarationCasingFixer - do not require T_STRING present in code

[kubawerlos]

No description provided.

[coveralls]

Pull Request Test Coverage Report for Build 4378332883

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 92.91%

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Totals
Change from base Build 4357889410:	0.0%
Covered Lines:	22735
Relevant Lines:	24470

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💛 - Coveralls

[Wirone]

Suggested changes cover scenario for arrow function that IMHO should be fixed too, but it isn't:

Code build on input code must match expected code.
Failed asserting that two strings are identical.
Expected :'<?php return fn (callable $c): int => 1;'
Actual   :'<?php return fn (CALLABLE $c): INT => 1;'