disable multicast tests on AzureLinux

[wfurt]

related to #115502.

default AZL has firewall that blocks multicast.

[Copilot]

Pull Request Overview

This PR disables multicast tests on AzureLinux by introducing a new conditional check that excludes platforms where multicast functionality is not available or blocked. The change consolidates existing platform exclusions and adds AzureLinux to the list of platforms that cannot run multicast tests due to firewall restrictions.

Key Changes:

• Introduces a new CanRunMulticastTests property that consolidates platform checks for multicast test compatibility
• Replaces individual ConditionalFact and ActiveIssue attributes with a single unified condition
• Adds AzureLinux to the list of platforms excluded from multicast tests

Comments suppressed due to low confidence (1)

src/libraries/System.Net.Sockets/tests/FunctionalTests/SocketOptionNameTest.cs:20

• [nitpick] The property name CanRunMulticastTests uses a positive naming convention but is implemented with negation logic. Consider renaming to ShouldSkipMulticastTests or restructuring the logic to avoid double negation for better readability.

 private static readonly bool CanRunMulticastTests = !(PlatformDetection.IsNotWindowsNanoNorServerCore ||

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[rzikm]

LGTM

[ManickaP]

[ManickaP]

/ba-g failures unrelated

[jeffhandley]

/backport to release/9.0-staging

[github-actions]

Started backporting to release/9.0-staging: https://github.com/dotnet/runtime/actions/runs/17566620163