Increase limit of open Dependabot PRs

This should help avoiding the upper bound deps Maven Enforcer rule,
which requires Dependabot PRs to be merged in an exact order (first a
common transitive dependency, then the main dependency).

By increasing the limit we should have less dead locks that occur when
Dependabot opens a PR for a direct dependency, but can not open a PR for
the transitive dependency.

Author: ppkarwasz

.github/dependabot.yaml

@@ -25,6 +25,7 @@ registries:
 updates:
 - package-ecosystem: maven
   directory: "/"
+  open-pull-requests-limit: 10
   schedule:
     interval: "daily"
   target-branch: "2.x"
@@ -101,6 +102,7 @@ updates:
 
 - package-ecosystem: maven
   directory: "/"
+  open-pull-requests-limit: 10
   schedule:
     interval: "daily"
   target-branch: "main"