common/installation: Fix indentation in a block

This introduces no functional changes.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

Closes: #1736
Approved by: alexlarsson
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Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f