Upgrade spotbugs to 4.8.6 (#2295)

* Upgrade spotbugs

* Upgrade spotbugs

build.gradle

@@ -12,7 +12,7 @@ buildscript {
     dependencies {
         classpath 'com.android.tools.build:gradle:4.2.0'
         classpath 'me.tatarka:gradle-retrolambda:3.7.1'
-        classpath "gradle.plugin.com.github.spotbugs.snom:spotbugs-gradle-plugin:4.5.1"
+        classpath "com.github.spotbugs.snom:spotbugs-gradle-plugin:6.0.18"
     }
 }
 
@@ -49,6 +49,7 @@ subprojects {
         // Currently we only warn about issues and try to fix them as we go, but those aren't mission critical.
         spotbugs {
             ignoreFailures = true
+            toolVersion = '4.8.6'
         }
 
         tasks.withType(com.github.spotbugs.snom.SpotBugsTask ) {