Use JOBS again like macos.yml

.github/workflows/ubuntu.yml

@@ -36,13 +36,17 @@ jobs:
         run: |
           chmod go-w $HOME
           sudo chmod -R go-w /usr/share
+      - name: Set ENV
+        run: |
+          echo '##[set-env name=JOBS]'-j$((1 + $(nproc --all)))
       - run: autoconf
       - name: configure
         run: ./configure -C --disable-install-doc
-      - run: make -j$((1 + $(nproc --all)))
+      - run: make $JOBS
       - name: Tests
-        run: make -s TESTOPTS="-j$((1 + $(nproc --all))) -q --tty=no" ${{ matrix.test_task }}
+        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 != 'test-bundled-gems' && !contains(github.event.head_commit.message, '[ci skip]')
       # test-bundled-gems is separated for marking `continue-on-error` because it randomly fails.