chore: remove sample/test dependabot entries to reduce PR noise (kagent-dev#1741)

## Summary

- Remove the **Python (uv) — sample applications** dependabot entry
(covers `/python/samples/*` and `/go/core/test/e2e/agents/kebab`)
- Remove the **Docker — sample and test images** dependabot entry
(covers the same sample/test directories)

These two entries generate frequent low-value dependency update PRs for
sample apps and test fixtures, adding review fatigue without meaningful
security or stability benefit. Core package dependencies (Python
workspace, Docker production images) remain tracked.

## Test plan

- [x] Verify dependabot.yml is valid YAML and parses correctly
- [ ] Confirm remaining dependabot entries (GitHub Actions, Go modules,
Python workspace, npm, Docker core) are unchanged

Signed-off-by: Jaison Paul <paul.jaison@gmail.com>
Co-authored-by: Eitan Yarmush <eitan.yarmush@solo.io>

Author: jsonmp-k8

.github/dependabot.yml

@@ -80,35 +80,6 @@ updates:
           - "minor"
           - "patch"
 
-  # Python (uv) — sample applications
-  - package-ecosystem: "uv"
-    directories:
-      - "/python/samples/adk/basic"
-      - "/python/samples/openai/basic_agent"
-      - "/python/samples/crewai/poem_flow"
-      - "/python/samples/crewai/research-crew"
-      - "/python/samples/langgraph/currency"
-      - "/go/core/test/e2e/agents/kebab"
-    schedule:
-      interval: "weekly"
-      day: "monday"
-    open-pull-requests-limit: 5
-    labels:
-      - "dependencies"
-    commit-message:
-      prefix: "chore(deps):"
-    reviewers:
-      - "EItanya"
-      - "peterj"
-      - "yuval-k"
-    groups:
-      samples-minor-patch:
-        patterns:
-          - "*"
-        update-types:
-          - "minor"
-          - "patch"
-
   # npm — Next.js UI
   - package-ecosystem: "npm"
     directory: "/ui"
@@ -158,32 +129,3 @@ updates:
         update-types:
           - "minor"
           - "patch"
-
-  # Docker — sample and test images
-  - package-ecosystem: "docker"
-    directories:
-      - "/python/samples/adk/basic"
-      - "/python/samples/openai/basic_agent"
-      - "/python/samples/crewai/poem_flow"
-      - "/python/samples/crewai/research-crew"
-      - "/python/samples/langgraph/currency"
-      - "/go/core/test/e2e/agents/kebab"
-    schedule:
-      interval: "weekly"
-      day: "monday"
-    open-pull-requests-limit: 5
-    labels:
-      - "dependencies"
-    commit-message:
-      prefix: "chore(deps):"
-    reviewers:
-      - "EItanya"
-      - "peterj"
-      - "yuval-k"
-    groups:
-      docker-samples-minor-patch:
-        patterns:
-          - "*"
-        update-types:
-          - "minor"
-          - "patch"