Drop continue-on-error for make check

Like macos.yml, we don't need to ignore `make check` failure.

.github/workflows/ubuntu.yml

@@ -45,14 +45,13 @@ jobs:
       - name: configure
         run: ./configure -C --disable-install-doc
       - run: make $JOBS
-      # TODO: Remove `continue-on-error` once they become stable and also we have a notification for their failure.
       - name: make check
         run: make -s ${{ matrix.test_task }}
         env:
           TESTOPTS: "$JOBS -q --tty=no"
           MSPECOPT: "-ff" # not using `-j` because sometimes `mspec -j` silently dies
         if: matrix.test_task == 'check'
-        continue-on-error: true
+      # TODO: Remove `continue-on-error` once they become stable and also we have a notification for their failure.
       - name: make test-bundler/test-bundled-gems
         run: make -s ${{ matrix.test_task }}
         if: matrix.test_task != 'check'