Fixing test errors in test_ecn_config_update.py

[mramezani95]

When updating green_min_threshold, green_max_threshold, or green_drop_probability in WRED profiles for which wred_green_enable is false (or not set) using the apply-patch command, sometimes we see these errors:

ERR syncd#syncd: [none] SAI_API_PORT:_brcm_sai_cosq_gport_discard_set:6205 cosq gport discard set failed with error Invalid parameter (0xfffffffc)
ERR syncd#syncd: [none] SAI_API_QUEUE:_brcm_sai_qos_queue_wred_set:1760 sai cosq gport discard set failed with error -5.
ERR syncd#syncd: [none] SAI_API_WRED:_brcm_xgs_sai_reapply_wred_profile:882 Apply queue config failed with error -5.

This PR fixes this issue by modifying test_ecn_config_update.py to not generate JSON patches for WRED profiles for which wred_green_enable is false (or not set). After this fix, these tests passed on a device on which the same tests failed before the fix:

generic_config_updater/test_ecn_config_update.py::test_ecn_config_updates[replace-green_min_threshold] PASSED                                         [ 25%]
generic_config_updater/test_ecn_config_update.py::test_ecn_config_updates[replace-green_max_threshold] PASSED                                         [ 50%]
generic_config_updater/test_ecn_config_update.py::test_ecn_config_updates[replace-green_drop_probability] PASSED                                      [ 75%]
generic_config_updater/test_ecn_config_update.py::test_ecn_config_updates[replace-green_min_threshold,green_max_threshold,green_drop_probability] PASSED [100%]

[Copilot]

Pull request overview

This PR fixes test errors in test_ecn_config_update.py that occurred when updating WRED green parameters (green_min_threshold, green_max_threshold, green_drop_probability) for profiles where wred_green_enable is false. The fix prevents JSON patches from being generated for WRED profiles that don't have green WRED enabled, avoiding SAI API errors.

Changes:

• Modified determine_delta_values to accept wred_green_enabled parameter and return zero deltas when green WRED is disabled
• Added filtering logic to skip WRED profiles with wred_green_enable=false when generating JSON patches
• Introduced a pytest fixture for tmpfile management (replacing try-finally pattern)

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