Fix f-string syntax error in microsoft-graph-security-intel breaking Python 3.11

[Copilot]

api_handler.py used double quotes inside double-quoted f-strings (PEP 701, Python 3.12+ only), causing a SyntaxError on Python 3.11 that prevented the connector from starting.

Change

Extract observable.get("value", None) to a local variable before the f-string, making the code valid on Python 3.11+:

# Before (Python 3.12+ only)
params = f"$filter=emailSenderAddress eq '{observable.get("value", None)}'"
params = f"$filter={ioc_type} eq '{observable.get("value", None)}'"

# After
observable_value = observable.get("value", None)
params = f"$filter=emailSenderAddress eq '{observable_value}'"
params = f"$filter={ioc_type} eq '{observable_value}'"

Affected method: SentinelApiHandler.search_indicators in stream/microsoft-graph-security-intel/src/microsoft_graph_security_intel_connector/api_handler.py.