assistant tools: Fix running tests locally (#26914)

Without this, we running into the following error:

```
Running into this when running tests. Is this  
dyld[45041]: Library not loaded: @rpath/WebRTC.framework/WebRTC
  Referenced from: <B2EA63A5-994E-3FB0-A74B-C9C4F7E5C1EF> /Users/aguz/zed/zed/target/debug/deps/assistant_tools-522d7745dd439dfb
  Reason: no LC_RPATH's found
```

Thanks Piotr!

Release Notes:

- N/A

crates/assistant_tools/Cargo.toml

@@ -38,3 +38,4 @@ collections = { workspace = true, features = ["test-support"] }
 gpui = { workspace = true, features = ["test-support"] }
 language = { workspace = true, features = ["test-support"] }
 project = { workspace = true, features = ["test-support"] }
+workspace = { workspace = true, features = ["test-support"] }