refactor(CopyrightGarbage): Avoid using a SortedSet in memory

See #6235 for context.

Signed-off-by: Sebastian Schuberth <[email protected]>

Author: sschuberth

model/src/main/kotlin/config/CopyrightGarbage.kt

@@ -19,7 +19,9 @@
 
 package org.ossreviewtoolkit.model.config
 
-import java.util.SortedSet
+import com.fasterxml.jackson.databind.annotation.JsonSerialize
+
+import org.ossreviewtoolkit.utils.common.StringSortedSetConverter
 
 /**
  * A class that defines which Copyright statements are to be considered as garbage instead of real findings.
@@ -28,7 +30,8 @@ data class CopyrightGarbage(
     /**
      * A set of literal strings that identify garbage Copyright findings.
      */
-    val items: SortedSet<String> = sortedSetOf()
+    @JsonSerialize(converter = StringSortedSetConverter::class)
+    val items: Set<String> = emptySet()
 )
 
 fun CopyrightGarbage?.orEmpty(): CopyrightGarbage = this ?: CopyrightGarbage()