Fix dependency resolution for plugins in buildSrc

fixtures/buildsrc/plugin-in-buildsrc/kotlin/buildSrc/build.gradle.kts

@@ -0,0 +1,12 @@
+plugins {
+    `kotlin-dsl`
+}
+
+repositories {
+    jcenter()
+    gradlePluginPortal()
+}
+
+dependencies {
+    implementation("com.diffplug.spotless:spotless-plugin-gradle:3.28.1")
+}

fixtures/buildsrc/plugin-in-buildsrc/kotlin/buildSrc/src/main/kotlin/com.example/custom-spotless.gradle.kts

@@ -0,0 +1,11 @@
+package com.example
+
+plugins {
+    com.diffplug.gradle.spotless
+}
+
+spotless {
+    kotlin {
+        ktlint()
+    }
+}