CI: make unit-test-linux and unit-test-windows blocking — backlog cleared

Drops continue-on-error: true (and the TODO comments) from both
unit-test jobs. They were guarding against "currently-broken addon
unit modules (import failures, stale API usage)" that have since been
fixed by the merged plugin-registration / dep-declaration round
(gramps-project#875 WordleGramplet, gramps-project#876 SourceReferences, gramps-project#878 EditExifMetadata,
gramps-project#879 MongoDB, gramps-project#880 PhotoTaggingGramplet, gramps-project#869 SurnameMappingGramplet,
gramps#2299 ClipboardGramplet) plus the lint backlog (gramps-project#843, gramps-project#847-gramps-project#869).

Verified by the most recent fork CI run on
eduralph/addons-source:maintenance/gramps60 (sha 8aabdd4, 2026-05-18):
both Unit Tests (Linux) and Unit Tests (Windows) reported success.

Also clears two stale comments that referenced the removed flag:
- unit-test-linux's "Run per-addon unit tests" step: drop the
  trailing "Falls silently under continue-on-error." sentence.
- integration's requires_mod-validate step: collapse the now-moot
  "this is the blocking copy" rationale to a plain pointer at
  unit-test-linux.

The lone remaining continue-on-error is on addon-structure (line 70),
gated by the po/template.pot backlog. PRs gramps-project#838-gramps-project#841 were closed
without merge; per Eduard's call the po/template.pot check stays
non-blocking for now.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: eduralph

.github/workflows/ci.yml

@@ -150,9 +150,6 @@ jobs:
   unit-test-linux:
     name: Unit Tests (Linux)
     runs-on: ubuntu-latest
-    # Non-blocking until the currently-broken addon unit modules (import
-    # failures, stale API usage) are sorted out in follow-up PRs.
-    continue-on-error: true
     container:
       image: ghcr.io/${{ github.repository }}/gramps-ci:gramps60
     steps:
@@ -260,7 +257,7 @@ jobs:
         # shell: bash — the container's default shell is /bin/sh
         # (dash on python:3.12-slim), which does not support the
         # ${var//pattern/repl} and ${var%.py} parameter expansions
-        # used below. Falls silently under continue-on-error.
+        # used below.
         shell: bash
         env:
           PYTHONPATH: .
@@ -303,8 +300,6 @@ jobs:
   unit-test-windows:
     name: Unit Tests (Windows)
     runs-on: windows-latest
-    # Non-blocking for the same reason as unit-test-linux.
-    continue-on-error: true
     defaults:
       run:
         shell: bash -el {0}
@@ -484,9 +479,7 @@ jobs:
           fi
 
       - name: Validate requires_mod names against Gramps' dep gate
-        # See unit-test-linux for rationale. This is the blocking copy:
-        # integration-test does not set continue-on-error, so a wrong
-        # requires_mod name surfaces as a CI failure here.
+        # See unit-test-linux for rationale.
         shell: bash
         run: |
           python3 - <<'PY'