apt: tests: allow re-running digest test without clean-up

Files inside CARGO_TARGET_TMPDIR are only cleaned on `cargo clean`, so
tests that expect files to not exist need to cleanup themselves.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>

proxmox-apt/tests/repositories.rs

@@ -130,6 +130,9 @@ fn test_digest() -> Result<(), Error> {
 
     assert!(file.write().is_err());
 
+    // best-effort cleanup for re-builds without a `cargo clean` in between
+    let _ = std::fs::remove_dir_all(&write_dir);
+
     Ok(())
 }