Python: fix for fc stepwise

[eavanvalkenburg]

Motivation and Context

fixes #6333

Description

Contribution Checklist

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

[markwallace-microsoft]

Python 3.10 Test Coverage Report •

File	Stmts	Miss	Cover	Missing
semantic_kernel/connectors/ai/open_ai/services
open_ai_chat_completion_base.py	211	93	56%	97, 117, 142–146, 170, 174, 190–195, 211–240, 243–254, 272–279, 290–298, 314–321, 342, 350, 356–362, 374–380, 411, 450, 452–453, 458–463, 467–474, 496, 505–514
semantic_kernel/planners/function_calling_stepwise_planner
function_calling_stepwise_planner.py	110	42	62%	126–214, 248–253
TOTAL	6288	1041	83%

Python 3.10 Unit Test Overview

Tests	Skipped	Failures	Errors	Time
1341	1 💤	0 ❌	0 🔥	12.200s ⏱️