Completion does not always add StringNames when it should

[KoBeWi]

Tested versions

4.3 beta1

System information

Windows 10.0.19045 - Vulkan (Forward+) - dedicated NVIDIA GeForce GTX 1060 (NVIDIA; 31.0.15.4633) - Intel(R) Core(TM) i7-7700HQ CPU @ 2.80GHz (8 Threads)

Issue description

From #66481

godot_esGYh8dO4H.mp4

Seems like some methods use a different autocompletion type.

Steps to reproduce

0. Enable text_editor/completion/add_string_name_literals editor setting
1. Add _input() method in a script
2. Do event.is_action(
3. Notice how it suggests a plain String

Minimal reproduction project (MRP)

N/A

[dalexeev]

CC @MewPurPur @HolonProduction