feat(isMobilePhone): add Gabon (fr-GA) mobile phone validation

[kaminimangal]

What I did

Added mobile phone validation for Gabon (fr-GA)
to the isMobilePhone validator.

Changes

• Added fr-GA regex in src/lib/isMobilePhone.js
• Added valid and invalid test cases in test/validators.test.js

References

• Gabon country code: +241
• Mobile numbers start with 02-07

Closes #1761

Checklist

• PR contains only changes related; no stray files, etc.
• README updated (where applicable)
• Tests written (where applicable)
• References provided in PR (where applicable)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (e36b279) to head (3292f70).

Additional details and impacted files

@@            Coverage Diff            @@
##            master     #2700   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          114       114           
  Lines         2586      2586           
  Branches       656       656           
=========================================
  Hits          2586      2586           

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