Enable clippy::useless_conversion (#8767)

This PR enables the
[`clippy::useless_conversion`](https://rust-lang.github.io/rust-clippy/master/index.html#/useless_conversion)
rule and fixes the outstanding violations.

Release Notes:

- N/A

crates/collab/src/tests/channel_tests.rs

@@ -1431,7 +1431,7 @@ fn assert_channels(
                 .ordered_channels()
                 .map(|(depth, channel)| ExpectedChannel {
                     depth,
-                    name: channel.name.clone().into(),
+                    name: channel.name.clone(),
                     id: channel.id,
                 })
                 .collect::<Vec<_>>()