Update tracecontext integration test gitref

[jomcgi]

Description

We're currently using an outdated version of the W3C test, this results in warnings in CI.
Updated gitref in scripts/tracecontext-integration-test.sh to latest from wc3/trace-context.
Skipped changed test that is incompatible with our implementation (we drop duplicated keys which is optional in the spec).
Added fixme comment to track setting flags for the test suite when they are available (wc3 issue)

Fixes #4105
Closes #4109

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• Executed test suite locally

Does This PR Require a Contrib Repo Change?

• No.

Checklist:

• Followed the style guidelines of this project
• Changelogs have been updated
• Unit tests have been added
• Documentation has been updated

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: jomcgi / name: Joe McGinley (91c3114)

[jomcgi]

Apologies this is my first PR - tests were passing locally but are failing in CI with tox.
There are some options for upgrading and resolving the error:

1. Reduce strictness level to 1 (skips this test but we also lose other coverage that matches our implementation)
2. Filter tests - bash or python processing to extract tests we would like to run
3. Wait for W3C issue to be resolved (unknown timeline) so that flags are properly supported

Option 2 works with:

TEST_TO_IGNORE="test_tracestate_duplicated_keys"
FILTERED_TESTS=$(python -c "
import unittest

from test import TraceContextTest

tests = unittest.TestLoader().loadTestsFromTestCase(TraceContextTest)
test_names = [
    f'TraceContextTest.{t._testMethodName}'
    for t in tests
    if t._testMethodName != '${TEST_TO_IGNORE}'
]
print(' '.join(test_names))
"  | grep "TraceContextTest")
python test.py http://127.0.0.1:5000/verify-tracecontext AdvancedTest TraceContext2Test $FILTERED_TESTS

Guidance would be appreciated - I can follow up with whatever is recommended.

[emdneto]

Apologies this is my first PR - tests were passing locally but are failing in CI with tox.

How tests passed locally?