Remove python 3.6 from CI

Author: NaderAlAwar

.github/workflows/linux-ci.yml

@@ -14,7 +14,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: [3.6, 3.7, 3.8, 3.9, 'pypy-3.6', 'pypy-3.7']
+        python-version: [3.7, 3.8, 3.9, 'pypy-3.6', 'pypy-3.7']
         kokkos-branch: ['master', 'develop']
 
     steps: