Replace debug_assert! with assert! in Signature::check_names (#11937)

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Debug assertions don't run at release, which means that `cargo test
--release` fails because the tests for name checks don't run properly.
These checks are not really expensive, and there shouldn't be any
noticeable difference to startup time, so there isn't much reason not to
just leave them in.

It's valuable to be able to run `cargo test --release`, as that can
expose race conditions and dependencies on undefined behavior that
aren't exposed in debug builds.

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This shouldn't affect anything. Any violations of this rule were being
caught with debug tests, which are run by the CI.

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crates/nu-protocol/src/signature.rs

@@ -471,7 +471,7 @@ impl Signature {
     /// Panics if one of them is found
     fn check_names(&self, name: impl Into<String>, short: Option<char>) -> (String, Option<char>) {
         let s = short.map(|c| {
-            debug_assert!(
+            assert!(
                 !self.get_shorts().contains(&c),
                 "There may be duplicate short flags for '-{}'",
                 c
@@ -481,7 +481,7 @@ impl Signature {
 
         let name = {
             let name: String = name.into();
-            debug_assert!(
+            assert!(
                 !self.get_names().contains(&name.as_str()),
                 "There may be duplicate name flags for '--{}'",
                 name