CI: a skipped integration_tests step reports the job as green

[randy-cro]

Problem

integration_tests is diff-gated (.github/workflows/test.yml):

- uses: technote-space/get-diff-action@v6.1.2
  with:
    PATTERNS: |
      **/**.sol
      **/**.go
      go.mod
      go.sum
      tests/integration_tests/**
- name: Run integration tests
  run: make run-integration-tests
  if: env.GIT_DIFF

When GIT_DIFF is empty the step is skipped, and a skipped step still makes the job report success. As a required check, that is indistinguishable from a real pass.

Effect

Every dependency bump reports integration_tests (unmarked): success without running anything. Between 2026-07-30 and 2026-09-16 the suite did not execute on develop at all, yet the branch showed green the whole time:

success   Run technote-space/get-diff-action@v6.1.2
skipped   Run integration tests

(from run 34244306239, develop @ 2253b15)

Because the suite also pulls its fixtures from upstream ethereum/execution-apis, real breakage accumulated invisibly and then failed on the next PR that happened to touch a .go file — #1099, whose diff had nothing to do with it.

Suggested fix

Make "did not run" distinguishable from "passed". Options:

1. A final aggregation job that the branch protection requires, which asserts each upstream job actually ran rather than treating skipped as satisfied.
2. Drop the path filter for jobs used as required checks, and control cost with concurrency/caching instead.
3. Keep the filter but have the job fail when it is required and GIT_DIFF is empty.

Related: #1101 (stale results satisfying the gate). The fixture pin in #1100 removes the upstream moving target but leaves this reporting hole.

[randy-cro]

Closing for now — not blocking, and #1100 does not address it. The diagnosis is preserved above if this becomes worth revisiting.