Bash tool breaks on NixOS with version >=1.0.49

### Describe the bug

Bash tool breaks on NixOS when updated to version >=1.0.49 (also present on 1.0.50). When the agent tries to run any command, it errors with:
```

```

Running copilot-cli with strace -f gives the following output:
```
[pid 2803] execve("/bin/bash", ["/bin/bash", "--norc", "--noprofile"], 0x5480bd70 /* 75 vars */
```
This seems to be the only relevant syscall related to the tool call.

NixOS does not have `/bin/bash`, only `/bin/sh`.

### Affected version

GitHub Copilot CLI 1.0.50.

### Steps to reproduce the behavior

1. Start a session, tell the agent to run anything in a shell.

### Expected behavior

1. The command gets executed.

### Additional context

_No response_

Reproduce the failure on NixOS by starting a session and asking the agent to run a shell command, then inspect the Bash tool's process-launch entry point. Use the reported strace execve call as the starting clue; done means shell commands execute successfully on NixOS versions 1.0.49 and later without the missing /bin/bash failure.

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