Add back python executable in test_env_unittest.py

http://crrev.com/c/2229335 added Python3 support for the `test_env_unittest.py`
files, but appears to have broken the test on Windows in the process.

Fixing by adding back `sys.executable` in the command to run, as Windows
doesn't support running scripts via shebang.

Bug: 942720
Change-Id: I40757a78ad707f36481e2906251ee8451aa89318
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2238269
Reviewed-by: Ben Pastene <[email protected]>
Reviewed-by: Dirk Pranke <[email protected]>
Commit-Queue: Dirk Pranke <[email protected]>
Cr-Commit-Position: refs/heads/master@{#776726}
diff --git a/testing/test_env_user_script.py b/testing/test_env_user_script.py
index 23f55cf..1d943876 100755
--- a/testing/test_env_user_script.py
+++ b/testing/test_env_user_script.py
@@ -6,6 +6,7 @@
 """Script for use in test_env unittests."""
 
 import os
+import sys
 
 import test_env
 
@@ -13,4 +14,4 @@
 TEST_SCRIPT = os.path.join(HERE, 'test_env_test_script.py')
 
 if __name__ == '__main__':
-  test_env.run_command([TEST_SCRIPT])
+  test_env.run_command([sys.executable, TEST_SCRIPT])