Closes #46801

When connecting to WSL2 with fish as the default shell, Zed gets stuck
at "Starting proxy". The connection works fine when bash is the default
shell.

In `start_proxy()`, the WSL command was being invoked with:

```rust
let proxy_process = match wsl_command_impl(&self.connection_options, "env", &proxy_args, false)
```

Changing the last argument to true invokes the WSL command with `--exec`
flag which executes the command in the WSL environment without spawning
a new shell.

With above fix I can launch Zed from WSL (Arch) with fish.