ci: make compat-matrix engine-job failures fail the run (#3376)

Removes continue-on-error from the tests job now that the debt gate is
cleared: PR #3365 merged and dispatch run 30976993285 on develop came back
fully green (all 5 engine jobs, aggregate 6 oracle soft-fails only, which
stay non-blocking via SOFT_FAIL_DBS under #2663). The rustcfml job keeps
its continue-on-error — it is an informational lane by design.

From now on a red engine leg turns the weekly run banner red instead of
being silently swallowed.

Signed-off-by: Peter Amiri <petera@pai.com>
Co-authored-by: Peter Amiri <petera@pai.com>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

Author: 3 people

.github/workflows/compat-matrix.yml

@@ -15,7 +15,6 @@ jobs:
   tests:
     name: "${{ matrix.cfengine }}"
     runs-on: ubuntu-latest
-    continue-on-error: true
     strategy:
       fail-fast: false
       matrix: