Python: Add missing index in Bedrock FunctionCallContent instantiation

[ja-bot]

Motivation and Context

Description

• Closes #12202

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 :smile:

[moonbox3]

@ja-bot, thanks for your contribution. Please fill out the Motivation and Context / Description sections in the PR description.

[markwallace-microsoft]

Python Unit Test Overview

Tests	Skipped	Failures	Errors	Time
3595	18 :zzz:	0 :x:	0 :fire:	1m 46s :stopwatch:

[ja-bot]

@ja-bot, thanks for your contribution. Please fill out the Motivation and Context / Description sections in the PR description.

Done @moonbox3. Please, let me know if something is not clear. Thanks!