fix(m365): move KNOWN_PLATFORMS to entra_service and normalize case

Move the constant from the check module to the service module so it
can be reused, and switch to a lowercase frozenset for
case-insensitive comparison.

prowler/providers/m365/services/entra/entra_conditional_access_policy_unknown_device_blocked/entra_conditional_access_policy_unknown_device_blocked.py

@@ -1,12 +1,11 @@
 from prowler.lib.check.models import Check, CheckReportM365
 from prowler.providers.m365.services.entra.entra_client import entra_client
 from prowler.providers.m365.services.entra.entra_service import (
+    KNOWN_PLATFORMS,
     ConditionalAccessGrantControl,
     ConditionalAccessPolicyState,
 )
 
-KNOWN_PLATFORMS = {"android", "iOS", "windows", "macOS", "linux"}
-
 
 class entra_conditional_access_policy_unknown_device_blocked(Check):
     """Check if at least one Conditional Access policy blocks unknown device platforms.

prowler/providers/m365/services/entra/entra_service.py

@@ -1004,6 +1004,9 @@ class PlatformConditions(BaseModel):
         allow_population_by_field_name = True
 
 
+KNOWN_PLATFORMS = frozenset({"android", "ios", "windows", "macos", "linux"})
+
+
 class TransferMethod(Enum):
     """Transfer methods for authentication flows in Conditional Access policies."""