When updating signatures, copy buildSrc deps to root project

a workaround for https://github.com/gradle/gradle/issues/24822

Bug: 278890578

Change-Id: I90d15bd8022880aa52afb11bf852875471734e12
diff --git a/build.gradle b/build.gradle
index 3a6b8e5..fc4788f 100644
--- a/build.gradle
+++ b/build.gradle
@@ -25,3 +25,9 @@
 apply from: "buildSrc/dependencies.gradle"
 
 apply plugin: AndroidXRootPlugin
+
+// workaround for https://github.com/gradle/gradle/issues/24822
+if (project.hasProperty("androidx.update.signatures")) {
+    apply plugin: "java-library"
+    apply from: "buildSrc/shared-dependencies.gradle"
+}