test(tvix): Fix tvix tests on macOS

Prior to this, some tests would not build
or would fail in an obscure way.

Change-Id: I68587cc7592492ebfd71ca02fc7ccc9ff7c0196f
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11544
Tested-by: BuildkiteCI
Reviewed-by: flokli <flokli@flokli.de>

tvix/eval/tests/nix_oracle.rs

@@ -30,7 +30,14 @@ fn nix_eval(expr: &str, strictness: Strictness) -> String {
         .arg(format!("({expr})"))
         .env(
             "NIX_REMOTE",
-            format!("local?root={}", store_dir.path().display()),
+            format!(
+                "local?root={}",
+                store_dir
+                    .path()
+                    .canonicalize()
+                    .expect("valid path")
+                    .display()
+            ),
         )
         .output()
         .unwrap();