ci / break unittest job into small job files

.github/workflows/unittest_linux.yml

@@ -0,0 +1,13 @@
+name: linux
+on:
+  push:
+    paths-ignore:
+    - 'docs/**'
+
+jobs:
+  linux:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v1
+    - name: make test_make
+      run: make test_make