Fix PHP 8.5 deprecation

[grzybu]

Fixes: Using null as an array offset is deprecated, use an empty string instead in PhoneNumberUtil:getRegionCodeForNumber

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.94%. Comparing base (674d187) to head (5a1cbbd).
⚠️ Report is 25 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #734      +/-   ##
============================================
- Coverage     85.99%   85.94%   -0.05%     
- Complexity     1303     1304       +1     
============================================
  Files            31       31              
  Lines          3484     3430      -54     
============================================
- Hits           2996     2948      -48     
+ Misses          488      482       -6     

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[giggsey]

Thanks!

I'm expecting a libphonenumber release from Google within the next few days, so this will go out as part of that. I'll also apply the same fix to libphonenumber-for-php-lite