[skip ci] add missing github pre release repo

Author: jdaugherty

examples/spring-boot-hibernate/build.gradle

@@ -2,6 +2,16 @@ buildscript {
     repositories {
         mavenCentral()
         maven { url "https://repo.grails.org/grails/core" }
+        if (System.getenv("GITHUB_MAVEN_PASSWORD") && !grailsVersion.endsWith('-SNAPSHOT')) {
+            System.out.println("Adding Grails Core Repo for ${project.name}")
+            maven {
+                url = 'https://maven.pkg.github.com/grails/grails-core'
+                credentials {
+                    username = 'DOES_NOT_MATTER'
+                    password = System.getenv("GITHUB_MAVEN_PASSWORD")
+                }
+            }
+        }
     }
     dependencies {
         classpath platform("org.grails:grails-bom:$grailsVersion")