Remove sealed from ScopedCache abstract class (#112)

(Backporting #93 to ZIO2 branch)

Co-authored-by: Adam Fraser <[email protected]>

Author: guizmaii

zio-cache/shared/src/main/scala/zio/cache/ScopedCache.scala

@@ -8,7 +8,7 @@ import java.util
 import java.util.concurrent.atomic.{AtomicBoolean, AtomicInteger, LongAdder}
 import scala.jdk.CollectionConverters._
 
-sealed abstract class ScopedCache[-Key, +Error, +Value] {
+abstract class ScopedCache[-Key, +Error, +Value] {
 
   /**
    * Returns statistics for this cache.