[CI] Fix NSIS downgrade step

**Describe the bug**

<img width="1594" height="324" alt="Image" src="https://github.com/user-attachments/assets/9c2b1f33-8878-44db-901c-9d1c5b64720d" />

**Expected behavior**
NSIS should be downgraded so that it doesn't trigger A/V scanner false positives.

**Actual behavior**
Installation fails and the default NSIS 3.10 will be used.
