Graph node enums resetting to default value after reload.

[cullumi]

Describe the bug
When directly creating non-default operation graph nodes (such as with SampleOp or VectorOp), saving does not back up the currently selected operation to the GaeaGraph's .tres file.

Makes #605 especially likely to happen with Operation nodes.

To Reproduce
Steps to reproduce the behavior:

1. Go to a Gaea Graph.
2. Create a Scalar Smoothstep SampleOp node.
3. Save.
4. Reload Project.
5. Open the same Gaea Graph. The SampleOp you created is now set to the Add operation.
6. Repeat, but on step 2 create a base Scalar SampleOp and set its operation to Scalar Smoothstep. Bug does not appear.

Expected behavior
The operation should never change back its default regardless of how you create it.

Godot Version
Godot v4.6.1 (stable win64)

Gaea Version
v2.0.0-beta6