ci: Limit scope of unittest to one python version (pytorch#2256)

Summary:
Pull Request resolved: pytorch#2256

Limits scope of unittesting to one python version for both macOS and
Windows. These types of workflows are particularly expensive and take a
long time so running them on every PR / every push is a bit wasteful
considering the value in signal between different python versions is
probably negligible.

Signed-off-by: Eli Uriegas <[email protected]>

Test Plan: Imported from OSS

Reviewed By: mthrok

Differential Revision: D34459626

Pulled By: seemethere

fbshipit-source-id: 47f5c317027f1b395edf9c1720b1b33ba689cad5

Author: seemethere

.circleci/config.yml

@@ -210,6 +210,14 @@ def indent(indentation, data_list):
     return ("\n" + " " * indentation).join(yaml.dump(data_list).splitlines())
 
 
+def unittest_python_versions(os):
+    return {
+        "windows": PYTHON_VERSIONS[:1],
+        "macos": PYTHON_VERSIONS[:1],
+        "linux": PYTHON_VERSIONS,
+    }.get(os)
+
+
 def unittest_workflows(indentation=6):
     jobs = []
     jobs += build_download_job(None)
@@ -218,7 +226,7 @@ def unittest_workflows(indentation=6):
             if os_type == "macos" and device_type == "gpu":
                 continue
 
-            for i, python_version in enumerate(PYTHON_VERSIONS):
+            for i, python_version in enumerate(unittest_python_versions(os_type)):
                 job = {
                     "name": f"unittest_{os_type}_{device_type}_py{python_version}",
                     "python_version": python_version,