Rename temp.rs to temp_home.rs (#563)

This file contains a test utility "TempHome" to create a temporary HOME
environment. "temp" is a really bad file name..

git_xet/src/test_utils/mod.rs

@@ -1,7 +1,7 @@
-mod temp;
+mod temp_home;
 mod test_repo;
 
 #[cfg(test)]
-pub use temp::TempHome;
+pub use temp_home::TempHome;
 #[cfg(test)]
 pub use test_repo::TestRepo;