don't force target-dir (cargo-miri already deconflicts that)

ui_test/src/dependencies.rs

@@ -43,9 +43,7 @@ pub fn build_dependencies(config: &Config) -> Result<Dependencies> {
     };
 
     setup_command(&mut build);
-    build
-        .arg("--target-dir=target/test_dependencies")
-        .arg("--message-format=json");
+    build.arg("--message-format=json");
 
     let output = build.output()?;
 

ui_test/src/lib.rs

@@ -54,7 +54,7 @@ pub struct Config {
 pub struct DependencyBuilder {
     pub program: PathBuf,
     pub args: Vec<String>,
-    pub envs: Vec<(String, String)>,
+    pub envs: Vec<(String, OsString)>,
 }
 
 #[derive(Debug)]