utils: Ensure that testing unset CARGO_HOME unsets it

In order to isolate this test from the test environment, if it
is attempting to determine behaviour when the CARGO_HOME environment
variable isn't present, it should ensure it's not present.

Signed-off-by: Daniel Silverstone <dsilvers@digital-scurf.org>

src/utils/utils.rs

@@ -767,6 +767,7 @@ mod tests {
     #[test]
     fn test_cargo_home() {
         // CARGO_HOME unset, we'll get the default ending in /.cargo
+        env::remove_var("CARGO_HOME");
         let cargo_home1 = cargo_home();
         let ch = format!("{}", cargo_home1.unwrap().display());
         assert!(ch.contains("/.cargo"));