Allow unwrap() in tests when clippy::unwrap_used is denied (#11616)

## Problem

The proxy denies using `unwrap()`s in regular code, but we want to use
it in test code
and so have to allow it for each test block.

## Summary of changes

Set `allow-unwrap-in-tests = true` in clippy.toml and remove all
exceptions.

proxy/src/cache/endpoints.rs

@@ -259,7 +259,6 @@ impl EndpointsCache {
 }
 
 #[cfg(test)]
-#[expect(clippy::unwrap_used)]
 mod tests {
     use super::*;
 

proxy/src/cache/project_info.rs

@@ -585,7 +585,6 @@ impl Cache for ProjectInfoCacheImpl {
 }
 
 #[cfg(test)]
-#[expect(clippy::unwrap_used)]
 mod tests {
     use super::*;
     use crate::scram::ServerSecret;