Update mypy to 2.1.0 in syntax tests workflow

Matches QuantConnect/Lean#9566.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: AlexCatarino

.github/workflows/syntax-tests.yml

@@ -48,7 +48,7 @@ jobs:
 
       - name: Run Syntax Test
         run: |
-          runInContainer bash -c "pip install --no-cache-dir quantconnect-stubs requests types-requests==2.32.* types-pytz==2025.2.0.* mypy==1.20.2"
+          runInContainer bash -c "pip install --no-cache-dir quantconnect-stubs requests types-requests==2.32.* types-pytz==2025.2.0.* mypy==2.1.0"
           runInContainer python -u project-templates/python/run_syntax_check.py
 
       - name: Run Project Match Check