[Security Solution] Incorrect field count in Rule Upgrade flyout

[pborgonovi]

Related to: #200904

Summary

Describe the bug:

When reviewing rule updates in the Update Flyout, the conflict message incorrectly displays the total number of fields with update conflicts. The message consistently shows a count of Fields + 1, regardless of the actual number of conflicting fields.

Kibana/Elasticsearch Stack version:

8.x

Current branch: 8.x  
Latest commit: d0c9a2f1f52 - [8.x] [Stack Monitoring / Logs] Fix Stack Monitoring logs links (#200043) (#200227)  
Remote tracking: origin/8.x  
Status relative to remote: up to date (no pending commits)  

Steps to reproduce:

1. Open the Rule Updates table.
2. Select a rule with conflicting fields and click to review the update.
3. Observe the Update Flyout conflict message at the top of the page.

Current behavior:
The conflict messages states:

• "Upgrade has X fields"
• “X of the fields have an update conflict, please review the suggested update being updating.”

Where X = Actual fields + 1.

Expected behavior:
The conflict message should accurately reflect the actual number of conflicting fields.

Screenshots

[elasticmachine]

Pinging @elastic/security-solution (Team: SecuritySolution)

[elasticmachine]

Pinging @elastic/security-detection-rule-management (Team:Detection Rule Management)

[elasticmachine]

Pinging @elastic/security-detections-response (Team:Detections and Resp)

[banderror]

@pborgonovi This one should have been fixed by @maximpn in #201501

[pborgonovi]

Retested with latest changes and it looks good: