tests: Explicitly specify a /tmp directory

Explicitly specify a /tmp directory, this fixes an issue on macOS where the
default tmp path that gets used could be very long, causing unix domain socket
tests to fail due to path length.

Signed-off-by: Matej Hrica <mhrica@redhat.com>

Author: mtjhrc

tests/runner/src/main.rs

@@ -188,7 +188,7 @@ fn run_tests(
             fs::create_dir_all(&path).context("Failed to create base directory")?;
             path
         }
-        None => TempDir::new("libkrun-tests")
+        None => TempDir::new_in("/tmp", "libkrun-tests")
             .context("Failed to create temp base directory")?
             .into_path(),
     };