[MINOR] [CORE] Fixes minor variable name typo

Author: Cheng Lian <lian@databricks.com>

Closes #8784 from liancheng/typo-fix.

core/src/test/scala/org/apache/spark/serializer/GenericAvroSerializerSuite.scala

@@ -76,9 +76,9 @@ class GenericAvroSerializerSuite extends SparkFunSuite with SharedSparkContext {
   test("caches previously seen schemas") {
     val genericSer = new GenericAvroSerializer(conf.getAvroSchema)
     val compressedSchema = genericSer.compress(schema)
-    val decompressedScheam = genericSer.decompress(ByteBuffer.wrap(compressedSchema))
+    val decompressedSchema = genericSer.decompress(ByteBuffer.wrap(compressedSchema))
 
     assert(compressedSchema.eq(genericSer.compress(schema)))
-    assert(decompressedScheam.eq(genericSer.decompress(ByteBuffer.wrap(compressedSchema))))
+    assert(decompressedSchema.eq(genericSer.decompress(ByteBuffer.wrap(compressedSchema))))
   }
 }