Bug located in ... app.open(file) for version 261

### 🔍 Before submitting the issue

- [x] I have searched among the existing issues
- [x] I am using a Python virtual environment

### 🐞 Description of the bug

The app.open(file) command does not work for 261.
I have proved it works for 242 and 252.

### 📝 Steps to reproduce

```
from ansys.mechanical.core import App
app=App(version=261, globals=globals())
print(app)
file=r"path\to\file\SYS.mechdb"
print(file)
app.open(file)
print(app)
allbodies = Model.GetChildren(DataModelObjectCategory.Body,True)
print(allbodies.Count)
```

### 💻 Which operating system are you using?

Windows

### 📀 Which ANSYS version are you using?

2026R1

### 🐍 Which Python version are you using?

3.13

### 📦 Installed packages

```shell
ansys-api-mechanical==0.1.4
ansys-mechanical-core==0.12.6
ansys-mechanical-stubs==0.1.10
ansys-pythonnet==3.1.0rc6
ansys-tools-common==0.5.0
appdirs==1.4.4
certifi==2026.2.25
cffi==2.0.0
charset-normalizer==3.4.7
click==8.3.2
clr_loader==0.2.10
colorama==0.4.6
grpcio==1.80.0
idna==3.11
platformdirs==4.9.6
protobuf==7.34.1
psutil==7.2.2
pycparser==3.0
requests==2.33.1
scooby==0.11.0
tqdm==4.67.3
typing_extensions==4.15.0
urllib3==2.6.3
```

Start by reproducing the provided app.open(file) example on Windows with Python 3.13 and compare version 261 against 242 and 252. Trace the app.open entry point and verify that the SYS.mechdb file opens and that Model.GetChildren returns the expected bodies.

Written by the indexing model from the issue text.