mirage/mirage: PR #1647: only print the 'adding unit argument' hint when configuring

@456844c

Stages:

• ❌ x86_64-debian-13-4.14 (2m12s)
• ❌ arm64-debian-13-4.14 (1m58s)
• ❌ x86_64-debian-13-5.4 (2m52s)
• ❌ arm64-debian-13-5.4 (1m52s)

History:

• 31/07/2026 15:49 ❌ @456844c (3m46s)