CI: build and run the unit tests in the Windows job again

7c6a0411d set PACKAGE_TESTS=OFF in windows-build.yml to make the job
green again. The job had turned red because three tests merged on
2026-10-07 (tst_toolbarsettings, tst_diagramtoolbarsettings,
tst_gesturesettings) set no settings scope, so QSettings on Windows had
no registry key and they failed. #1411 gives them their scope. With
PACKAGE_TESTS=OFF the "Run the unit tests" step finds no tests and
still succeeds, so the job checks nothing.

Set PACKAGE_TESTS back to ON.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Beat Hangartner <beat@hangartners.ch>

.github/workflows/windows-build.yml

@@ -117,7 +117,7 @@ jobs:
             -DQT_VERSION_MAJOR=6 \
             -DBUILD_WITH_KF=ON \
             -DBUILD_KF=OFF \
-            -DPACKAGE_TESTS=OFF \
+            -DPACKAGE_TESTS=ON \
             -DCMAKE_POLICY_DEFAULT_CMP0077=NEW \
             -DCMAKE_POLICY_VERSION_MINIMUM=3.5 \
             -DQET_EXPORT_PROJECT_DB=ON \