GDScript test suite fails with MinGW-LLVM build

### Tested versions

v4.4.dev.custom_build [42a330e6e]

### System information

Godot v4.4.dev (42a330e6e) - Windows 10.0.22621 - Multi-window, 2 monitors - Vulkan (Forward+) - dedicated NVIDIA GeForce RTX 3060 Ti (NVIDIA; 32.0.15.6109) - AMD Ryzen 7 3700X 8-Core Processor (16 threads)

### Issue description

Toolchain used: https://github.com/mstorsjo/llvm-mingw/releases (both 20240917 with LLVM 19.1.0 final and llvm-mingw 20240619 with LLVM 18.1.8)

Output:
```
[doctest] doctest version is "2.4.11"
[doctest] run with "--help" for options
Could not load project settings.
ERROR: Could not open specified test directory.
at: (modules\gdscript\tests\gdscript_test_runner.cpp:334)
===============================================================================
./modules/gdscript/tests/gdscript_test_runner_suite.h:43:
TEST SUITE: [Modules][GDScript]
TEST CASE: Script compilation and runtime

modules\gdscript\tests\gdscript_test_runner.cpp:190: FATAL ERROR: An error occurred while making the tests.

./modules/gdscript/tests/gdscript_test_runner_suite.h:49: FATAL ERROR: REQUIRE( fail_count == 0 ) is NOT correct!
values: REQUIRE( -1 == 0 )
logged: Make sure `*.out` files have expected results.
All GDScript tests should pass.

ERROR: Failed to create file "res://.editorconfig".
at: EditorPaths (editor\editor_paths.cpp:271)
ERROR: Failed to get attributes for: res://.editorconfig
at: (drivers\windows\file_access_windows.cpp:473)
Could not load project settings.
===============================================================================
./modules/gdscript/tests/test_completion.h:223:
TEST SUITE: [Modules][GDScript][Completion]
TEST CASE: [Editor] Check suggestion list

./modules/gdscript/tests/test_completion.h:87: FATAL ERROR: Invalid test directory.

WARNING: Property not found: gui/theme/lcd_subpixel_layout
at: get_setting_with_override (core\config\project_settings.cpp:375)
===============================================================================
./modules/gdscript/tests/test_lsp.h:391:
TEST SUITE: [Modules][GDScript][LSP]
TEST CASE: [workspace][resolve_symbol]

./modules/gdscript/tests/test_lsp.h:90: FATAL ERROR: REQUIRE( err == OK ) is NOT correct!
values: REQUIRE( 31 == 0 )
logged: Could not open specified root directory

================================================================
CrashHandlerException: Program crashed with signal 11
Engine version: Godot Engine v4.4.dev.custom_build (de106b9cf3557cfc3dcccad5e62d46d845e32730)
Dumping the backtrace. Please include this when reporting the bug to the project developer.
[1] _gnu_exception_handler (../crt/crt_handler.c:0)
[2] GDScriptTests::initialize(String const&) (./modules/gdscript/tests/test_lsp.h:91)
-- END OF BACKTRACE --
================================================================
```

### Steps to reproduce

Build Godot using MinGW-LLVM (`use_mingw=yes` and `use_llvm=yes`) with tests enabled.
Run it with `--test`.

### Minimal reproduction project (MRP)

-

Start by reproducing the MinGW-LLVM build with use_mingw=yes and use_llvm=yes, then run Godot with --test. Inspect modules/gdscript/tests/gdscript_test_runner.cpp, test_completion.h, and test_lsp.h, focusing on the reported invalid or missing test directories and crash. Done means the GDScript test suites run successfully without directory or file errors or a crash.

Written by the indexing model from the issue text.