[v1.56.1] contrib/gofiber/fiber: upgrade to v2.50.0 and fix breaking change

[darccio]

What does this PR do?

Cherrypick #2277

Reviewer's Checklist

• Changed code has unit tests for its functionality at or near 100% coverage.
• There is a benchmark for any new code, or changes to existing code.
• If this interacts with the agent in a new way, a system test has been added.

For Datadog employees:

• If this PR touches code that handles credentials of any kind, such as Datadog API keys, I've requested a review from @DataDog/security-design-and-guidance.
• This PR doesn't touch any of that.

Unsure? Have a question? Request a review!

[pr-commenter]

Benchmarks

Benchmark execution time: 2023-10-19 15:30:24

Comparing candidate commit dafe6b5 in PR branch dario.castane/v1.56.1-fiber with baseline commit 5781af2 in branch release-v1.56.x.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 40 metrics, 1 unstable metrics.