Silence clippy warnings about #[cfg(not(test))]

It doesn't seem possible to disable the warning with an outer attribute,
and using an inner attribute would cause inconsistent linting across
files.  Just disable the warning everywhere; presumably when we exclude
code from test builds we do it intentionally.

https://rust-lang.github.io/rust-clippy/master/index.html#cfg_not_test

Author: bgilbert

Cargo.toml

@@ -175,6 +175,7 @@ absolute_paths = "allow"
 as_conversions = "allow"
 arithmetic_side_effects = "allow"
 bool_to_int_with_if = "allow"
+cfg_not_test = "allow"
 default_numeric_fallback = "allow"
 else_if_without_else = "allow"
 expect_used = "allow"