Suppress Psalm UndefinedDocblockClass for Internal\RepeatedField

[bobstrecansky]

Summary

• Suppress Psalm UndefinedDocblockClass issues that reference
  Google\Protobuf\Internal\RepeatedField.

Why

google/protobuf 4.x deprecated Google\Protobuf\Internal\RepeatedField in
favor of Google\Protobuf\RepeatedField. The Internal class is now defined
as an if (false) { class RepeatedField extends \Google\Protobuf\RepeatedField {} } stub plus a runtime class_alias.
Psalm's static parser can see only the stub, not the alias, so getters on the
generated proto messages that return Internal\RepeatedField (e.g.
ExportMetricsServiceRequest::getResourceMetrics()) trigger
UndefinedDocblockClass on every Otlp converter file.

This is the same workaround pattern already used for offsetGet/offsetSet
on the same class. No source changes; once google/protobuf removes the
Internal stub entirely we can revisit.

Unblocks PHP QA on PHP 8.2/8.3/8.4 main builds.

Test plan

• PHP QA workflow goes green on 8.2/8.3/8.4

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 67.71%. Comparing base (471b51d) to head (845c4d0).

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1959      +/-   ##
============================================
- Coverage     67.75%   67.71%   -0.05%     
  Complexity     3044     3044              
============================================
  Files           459      459              
  Lines          8883     8883              
============================================
- Hits           6019     6015       -4     
- Misses         2864     2868       +4     

Flag	Coverage Δ
8.5	67.71% <ø> (-0.05%)	⬇️

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see 5 files with indirect coverage changes

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