fix: access rdkafka message headers with strings instead of symbols

[Ruto8]

For context, we're using both rdkafka-ruby and opentelemetry-ruby-contrib and we get a lot of warnings like this in the logs:

rdkafka deprecation warning: header access with Symbol key :traceparent treated as a String. Please change your code to use String keys to avoid this warning. Symbol keys will break in version 1.

I tracked it down to this line from rdkafka-ruby, where it seems they have deprecated accessing headers with Symbols.

In this PR, I removed the specific getter set to symbol_key_getter for the rdkafka consumer patch. This is also similar to what is done with ruby-kafka.

I believe the getter will default to text_map_getter, so we don't have to explicitly set it here.

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: Ruto8 / name: Paweł Rutkowski (6dc0a55)
• ✅ login: arielvalentin / name: Ariel Valentin (c942dc9, b1452ba, 229c7ac, 112f119)
• ✅ login: fbogsany / name: Francis Bogsanyi (8dba370)
• ✅ login: kaylareopelle / name: Kayla Reopelle (she/her) (27384c2)

[arielvalentin]

@Ruto8 Would you kindly take a look at this failing test?

https://github.com/open-telemetry/opentelemetry-ruby-contrib/actions/runs/6086303974/job/16513507151?pr=650

[Ruto8]

@Ruto8 Would you kindly take a look at this failing test?

@arielvalentin thank you for pointing this out. Unfortunately, the tests pass locally for me. I'm able to access the span, as expected. Can there be some differences between CI and local setup here? Is it possible it's a flaky test?

[arielvalentin]

Did you try running the test with the seed option that's failing?

Run options: --seed 35683

Or running the test in a loop to see if it's non-deterministic? Something like

for i in {1..20}; do
  bundle exec rake test
done

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[github-actions]

👋 This pull request has been marked as stale because it has been open with no activity. You can: comment on the issue or remove the stale label to hold stale off for a while, add the keep label to hold stale off permanently, or do nothing. If you do nothing this pull request will be closed eventually by the stale bot