Need to support cmake.testEnvironment

### Brief Issue Summary

https://github.com/microsoft/vscode-cmake-tools/blob/main/docs/debug-launch.md#gdb-1

Need environment variables for debugging.

### CMake Tools Diagnostics

```shell

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### Debug Log

```shell

```

### Additional Information

_No response_

Start with docs/debug-launch.md at the GDB section and trace how the extension currently builds debug launches. Check the existing configuration handling for cmake.testEnvironment; the work is done when users can provide environment variables for debugging and the behavior is covered by the relevant existing checks.

Written by the indexing model from the issue text.