Update eclipse-jdt.jsonnet

[jukzi]

disallow merge commits

eclipse-jdt/eclipse.jdt.ui#991 (comment)

[github-actions]

Diff for 8bb4164:

Printing local diff for configuration at '/home/runner/work/.eclipsefdn/.eclipsefdn/otterdog-configs/otterdog.json'

Actions are indicated with the following symbols:
+   create
!   modify
!   forced update
-   delete

Organization eclipse-jdt[id=eclipse-jdt]
  there have been 10 validation infos, enable verbose output with '-v' to to display them.

  
!   repository[name=".github"] {
!     allow_merge_commit                                       = true -> false
!   }
  
  Plan: 0 to add, 1 to change, 0 to delete.

Showing diff to a canonical version of the configuration at '/home/runner/work/.eclipsefdn/.eclipsefdn/otterdog-configs/otterdog.json'

Organization eclipse-jdt[id=eclipse-jdt]
--- original
+++ canonical
@@ -3,6 +3,7 @@
 orgs.newOrg('eclipse-jdt') {
   _repositories+:: [
     orgs.newRepo('.github') {
+      allow_merge_commit: false
       delete_branch_on_merge: false
       web_commit_signoff_required: false
       workflows+: {

[netomi]

the setting is live, however I noticed that you made the change for the .github repo while it should have probably been for the eclipse.jdt.ui repo (and for others probably as well).