try to prevent 'git' reading user and system configuration (#960)

Author: Byron

tests/tools/src/lib.rs

@@ -504,6 +504,8 @@ fn configure_command<'a>(
         .env_remove("GIT_DIR")
         .env_remove("GIT_ASKPASS")
         .env_remove("SSH_ASKPASS")
+        .env("GIT_CONFIG_SYSTEM", ":")
+        .env("GIT_CONFIG_GLOBAL", ":")
         .env("GIT_TERMINAL_PROMPT", "false")
         .env("GIT_AUTHOR_DATE", "2000-01-01 00:00:00 +0000")
         .env("GIT_AUTHOR_EMAIL", "author@example.com")