[SIEM][Detection Engine] Typo on Detection Engine page

[benskelker]

Kibana version: 8.0

Describe the bug: Typo on Detection Engine page when no SIEM indices are found.

Steps to reproduce:

1. Make sure no SIEM indices are configured
2. Navigate to the SIEM > Detection engine page

Screenshots (if relevant):

Should be:
It looks like you don’t have any indices relevant to the detection engine in the SIEM application

[elasticmachine]

Pinging @elastic/siem (Team:SIEM)