Python: fix discrimator field for CMC

[eavanvalkenburg]

Motivation and Context

Turns out we had a mistake in the way CMC discriminates content types, this PR fixes that

Description

Adds discriminator field to the item in the list rather then the list itself
Adds additional tests

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 Test Coverage Report

File	Stmts	Miss	Cover	Missing
semantic_kernel
kernel.py	199	47	76%	150, 161, 165, 315–318, 425, 439–482
semantic_kernel/agents/channels
open_ai_assistant_channel.py	49	1	98%	42
semantic_kernel/agents/group_chat
agent_chat.py	116	1	99%	91
agent_group_chat.py	67	2	97%	113, 135
broadcast_queue.py	72	1	99%	35
semantic_kernel/agents/open_ai
assistant_content_generation.py	68	2	97%	81–82
open_ai_assistant_base.py	361	3	99%	243, 321–322
semantic_kernel/connectors/ai/azure_ai_inference/services
azure_ai_inference_chat_completion.py	153	4	97%	177, 327–328, 444
semantic_kernel/connectors/ai/embeddings
embedding_generator_base.py	8	1	88%	50
semantic_kernel/connectors/ai/google
shared_utils.py	39	2	95%	97, 119
semantic_kernel/connectors/ai/google/google_ai/services
google_ai_chat_completion.py	152	4	97%	155, 267, 301–302
utils.py	63	3	95%	139, 157–162
semantic_kernel/connectors/ai/google/vertex_ai/services
utils.py	65	3	95%	141, 159–164
vertex_ai_chat_completion.py	152	4	97%	149, 260, 294–295
semantic_kernel/connectors/ai/hugging_face/services
hf_text_completion.py	54	3	94%	97, 105, 136
hf_text_embedding.py	32	5	84%	79–83
semantic_kernel/connectors/memory/azure_ai_search
azure_ai_search_collection.py	87	2	98%	150, 152
semantic_kernel/connectors/memory/redis
redis_collection.py	160	2	99%	146, 316
utils.py	45	11	76%	145–146, 164, 166, 173–188
semantic_kernel/connectors/openapi_plugin
openapi_manager.py	58	2	97%	110–111
openapi_parser.py	88	1	99%	127
openapi_runner.py	105	2	98%	181–182
semantic_kernel/connectors/openapi_plugin/models
rest_api_operation.py	129	1	99%	242
semantic_kernel/contents
function_call_content.py	97	1	99%	201
semantic_kernel/data
vector_store_record_collection.py	249	19	92%	410, 470–474, 482–486, 526–529, 536–539
vector_store_record_utils.py	26	2	92%	50, 52
semantic_kernel/functions
kernel_function_decorator.py	98	1	99%	102
kernel_function_from_method.py	96	1	99%	153
kernel_function_from_prompt.py	154	7	95%	165–166, 180, 201, 219, 239, 322
kernel_function_log_messages.py	36	6	83%	37–43
kernel_plugin.py	187	2	99%	472, 475
semantic_kernel/planners
plan.py	234	45	81%	54, 163–165, 197, 214–227, 264, 269, 277–278, 288–291, 308, 313, 329, 332–337, 355, 360, 363, 365, 372, 386–388, 393–397
semantic_kernel/planners/function_calling_stepwise_planner
function_calling_stepwise_planner.py	116	4	97%	145, 189–190, 198
semantic_kernel/planners/sequential_planner
sequential_planner.py	64	6	91%	71, 75, 109, 125, 134–135
sequential_planner_extensions.py	50	9	82%	31–32, 56, 110–124
sequential_planner_parser.py	77	12	84%	66–74, 93, 117–120
semantic_kernel/schema
kernel_json_schema_builder.py	119	5	96%	50, 84, 206, 210–211
semantic_kernel/template_engine/blocks
code_block.py	77	1	99%	119
named_arg_block.py	43	1	98%	98
semantic_kernel/utils/telemetry
user_agent.py	16	2	88%	18–19
semantic_kernel/utils/telemetry/model_diagnostics
decorators.py	105	2	98%	206, 210
TOTAL	10825	233	98%

Python Unit Test Overview

Tests	Skipped	Failures	Errors	Time
2386	1 💤	0 ❌	0 🔥	54.540s ⏱️