Isolate the memory startup metadata test from Git enrichment - #49000

## Why

Best-effort workspace enrichment can time out independently of the detached
request metadata checked by the memory startup test.

## What changed

Keep the phase-one service-tier and detached-metadata test fixture outside Git
and assert that `workspaces` is absent. Update the header assertion message to
refer to turn metadata.

GitOrigin-RevId: 9541668fc62a28d1ff3131d7f71b351149b6e152