Fix not keeping semantics of .optional on custom schema

Author: XiNiHa

core/src/main/scala-2/caliban/schema/SchemaDerivation.scala

@@ -100,7 +100,7 @@ trait CommonSchemaDerivation[R] {
                 val hasNonNullAnn  = p.annotations.contains(GQLNonNullable())
 
                 if (hasNonNullAnn) (false, false)
-                else if (hasNullableAnn || p.typeclass.nullable) (true, false)
+                else if ((hasNullableAnn || p.typeclass.optional) && !p.typeclass.canFail) (true, false)
                 else if (p.typeclass.canFail) (true, true)
                 else (false, false)
               }

core/src/main/scala-3/caliban/schema/DerivationUtils.scala

@@ -132,7 +132,7 @@ private object DerivationUtils {
         val hasNonNullAnn  = fieldAnnotations.contains(GQLNonNullable())
 
         if (hasNonNullAnn) (false, false)
-        else if (hasNullableAnn || schema.nullable) (true, false)
+        else if ((hasNullableAnn || schema.optional) && !schema.canFail) (true, false)
         else if (schema.canFail) (true, true)
         else (false, false)
       }