clippy: Suppress needless_pass_by_value in tests

Rationale: same as for useless_vec, as in 01cb7ee0a1.

Prompted by reading a commit where someone did makework to get rid of
an occurrence of this warning.

maint/add_warning

@@ -67,6 +67,7 @@ TEST_LINTS = """
 #![allow(clippy::unwrap_used)]
 #![allow(clippy::unchecked_duration_subtraction)]
 #![allow(clippy::useless_vec)]
+#![allow(clippy::needless_pass_by_value)]
 """
 
 # ---------- some notes about lints we might use - NOT USED by any code here ----------