Fix some tests that have the wrong expected exception message

The message got improved in a conflicting change to these tests being added.

kotlin/src/test/java/com/squareup/moshi/kotlin/KotlinJsonAdapterTest.kt

@@ -162,7 +162,7 @@ class KotlinJsonAdapterTest {
       jsonAdapter.fromJson("{\"a\":\"hello\"}")
       fail()
     } catch (expected: JsonDataException) {
-      assertThat(expected).hasMessage("Non-null value 'a' was null at \$")
+      assertThat(expected).hasMessage("Non-null value 'a' was null at \$.a")
     }
   }
 
@@ -190,7 +190,7 @@ class KotlinJsonAdapterTest {
       jsonAdapter.fromJson("{\"a\":\"hello\"}")
       fail()
     } catch (expected: JsonDataException) {
-      assertThat(expected).hasMessage("Non-null value 'a' was null at \$")
+      assertThat(expected).hasMessage("Non-null value 'a' was null at \$.a")
     }
   }