fix: Collect EnumerateUnmappedOrConfiguredTargetMembers to prevent collection was modified exception

[trejjam]

Collect EnumerateUnmappedOrConfiguredTargetMembers to prevent collection was modified exception

Description

Fixes #1403

Checklist

• The existing code style is followed
• The commit message follows our guidelines
• Performed a self-review of my code
• Hard-to-understand areas of my code are commented
• The documentation is updated (as applicable)
• Unit tests are added/updated
• Integration tests are added/updated (as applicable, especially if feature/bug depends on roslyn or framework version in use)

[latonz]

Thanks a lot for the quick fix 😊