Python: mypy coverage for template engine folder

[eavanvalkenburg]

Motivation and Context

Mypy coverage for template engines folder

Description

Contribution Checklist

• [x] The code builds clean without any errors or warnings
• [x] The PR follows the SK Contribution Guidelines and the pre-submission formatting script raises no violations
• [x] All unit tests pass, and I have added new tests where possible
• [x] I didn't break anyone :smile:

[markwallace-microsoft]

Python 3.10 Test Coverage Report •

File	Stmts	Miss	Cover	Missing
semantic_kernel/template_engine/blocks
code_block.py	70	1	99%	130
var_block.py	37	2	95%	79–80
TOTAL	5688	902	84%

Python 3.10 Unit Test Overview

Tests	Skipped	Failures	Errors	Time
1287	1 :zzz:	0 :x:	0 :fire:	14.039s :stopwatch:

[eavanvalkenburg]

merged into #6250