Fix invalid_namespace_member error description copy-paste error

[Copilot]

Addresses feedback on PR #670 regarding incorrect error message for invalid_namespace_member in app/services/error_code.rb.

Changes

• Fixed error description on line 54: changed "The flow setting is invalid" to "The namespace member is invalid"

# Before
invalid_namespace_member: { description: 'The flow setting is invalid because of active model errors' },

# After
invalid_namespace_member: { description: 'The namespace member is invalid because of active model errors' },

The error was a copy-paste artifact from the preceding invalid_flow_setting entry.

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