Temporary disable linux and all pythons execpt one to reduce the build matrix size

Author: sergregory

.github/workflows/build_wheels.yml

@@ -22,8 +22,8 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-latest, macos-latest]
-        python-version: [3.6, 3.7, 3.8, 3.9]
+        os: [macos-latest] # ubuntu-latest,
+        python-version: [3.8] # [3.6, 3.7, 3.8, 3.9]
         platform: [x64]
         with_contrib: [0, 1]
         without_gui: [0, 1]