When multiple molecule matrix runners share the same Docker host,
they conflict on the container name "ubuntu-2604" (409 Conflict
from Docker). This appends the MATRIX_INDEX as a suffix (e.g.
ubuntu-2604-r3) so each runner gets a unique container name.
Closes DEVX-148
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Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>