Selectively inherit yaml vars in stress trigger jobs

The parent's global RUNNER_SCRIPT_TIMEOUT: 55m was reaching the stress
and tsan:stress child pipelines via inherited yaml variables, where
inherited values outrank the child's job-level variables. That caused
stress jobs with BIND_STRESS_TESTS_RUN_TIME >= 60 to be killed at 55
minutes, regardless of the per-job RUNNER_SCRIPT_TIMEOUT set in the
generated child config.

Use inherit:variables with a positive list on both trigger jobs:
inherit only CI_REGISTRY_IMAGE so the parent's registry override
(needed for image pulls in the child) flows through, while keeping
RUNNER_SCRIPT_TIMEOUT (and other globals) out of the child pipeline's
variable scope. The per-job RUNNER_SCRIPT_TIMEOUT values set by the
generated child config now take effect.

Assisted-by: Claude:claude-opus-4-7
(cherry picked from commit 73915b73d1)

.gitlab-ci.yml

@@ -1631,6 +1631,13 @@ unit:clang:tsan:
 tsan:stress:
   <<: *default_triggering_rules
   stage: system
+  # In a downstream pipeline, yaml variables inherited from the parent outrank
+  # the child's job-level `variables:` block. Inherit only what the child
+  # actually needs (image lookup), so the parent's RUNNER_SCRIPT_TIMEOUT does
+  # not override the per-job values set in the generated child config.
+  inherit:
+    variables:
+      - CI_REGISTRY_IMAGE
   variables:
     PARENT_PIPELINE_ID: $CI_PIPELINE_ID
   trigger:
@@ -2365,6 +2372,13 @@ shotgun:doh-get:
 stress-test-child-pipeline:
   <<: *default_triggering_rules
   stage: performance
+  # In a downstream pipeline, yaml variables inherited from the parent outrank
+  # the child's job-level `variables:` block. Inherit only what the child
+  # actually needs (image lookup), so the parent's RUNNER_SCRIPT_TIMEOUT does
+  # not override the per-job values set in the generated child config.
+  inherit:
+    variables:
+      - CI_REGISTRY_IMAGE
   rules:
     - if: '$CI_MERGE_REQUEST_DIFF_BASE_SHA != null'
       changes: