Update springDocVersion to v2.8.6

Author: renovate[bot]

build.gradle

@@ -33,7 +33,7 @@ plugins {
 ext {
     // versions of dependencies
     springBootVersion = '3.4.3'
-    springDocVersion  = '2.8.5'
+    springDocVersion  = '2.8.6'
     javersVersion     = '7.8.0'
 }