[202511] [conditional_mark] Skip gnmi/test_gnmic.py (#24329)

[auspham]

Add a conditional-mark skip for tests/gnmi/test_gnmic.py while the gnmic binary is being removed from docker-ptf.

This is a precondition for the companion docker-ptf change that drops gnmic from the image. tests/gnmi/test_gnmic.py is the only test in this repo that invokes /usr/local/bin/gnmic directly (via PtfGnmic.capabilities()); without this skip, that test would start failing on the next docker-ptf rebuild.

Fixes # (issue): #24328

• Test case (verification of existing or new feature)

• Request back port to applicable release branches (master only — no behavior change for release branches that don't run this test)

Reduce docker-ptf supply-chain surface. gnoic was removed in sonic-buildimage#27055; gnmic is the next candidate because it has only one consumer in sonic-mgmt and that consumer can be skipped without losing coverage of any production behavior — gnmi_tls.gnoi.* and pygnmi cover the actual gNMI/gNOI surfaces under test.

Added an entry under the gnmi/ section of tests_mark_conditions.yaml that skips the test while #24328 is open. When the issue closes, the skip lifts — by then we should have either deleted the test outright or restored gnmic.

• yaml.safe_load parses the file cleanly with the new entry present.
• conditional_mark plugin uses pytest_collection_modifyitems; no test execution required to confirm marker application — the existing unit_test/ suite under tests/common/plugins/conditional_mark/ covers that mechanism.

None.

N/A — no test added.

N/A.

Description of PR

Summary:
Fixes # (issue)

Type of change

• Bug fix
• Testbed and Framework(new/improvement)
• New Test case
  • Skipped for non-supported platforms
• Test case improvement

Back port request

• 202205
• 202305
• 202311
• 202405
• 202411
• 202505
• 202511

Approach

What is the motivation for this PR?

How did you do it?

How did you verify/test it?

Any platform specific information?

Supported testbed topology if it's a new test case?

Documentation

[mssonicbld]

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