GDScript: Fix test for read-only state of constants

modules/gdscript/tests/scripts/runtime/errors/constant_array_push_back.gd

@@ -1,4 +0,0 @@
-const array: Array = [0]
-
-func test():
-	array.push_back(0)

modules/gdscript/tests/scripts/runtime/errors/constant_array_push_back.out

@@ -1,7 +0,0 @@
-GDTEST_RUNTIME_ERROR
->> ERROR
->> on function: push_back()
->> core/variant/array.cpp
->> 253
->> Condition "_p->read_only" is true.
->> Array is in read-only state.

modules/gdscript/tests/scripts/runtime/errors/constant_dictionary_erase.gd

@@ -1,4 +0,0 @@
-const dictionary := {}
-
-func test():
-	dictionary.erase(0)

modules/gdscript/tests/scripts/runtime/errors/constant_dictionary_erase.out

@@ -1,7 +0,0 @@
-GDTEST_RUNTIME_ERROR
->> ERROR
->> on function: erase()
->> core/variant/dictionary.cpp
->> 177
->> Condition "_p->read_only" is true. Returning: false
->> Dictionary is in read-only state.