[FIX][csharp-netcore] fixed anyOf/oneOf generating non-compilable code (null-coalescing operator on enum)

[Ikelio]

Fixes #13384

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[Ikelio]

Can we rerun the tests pls ? I can't see a reason for the csharp netcore .mustache changes to create a timeout during typescript tests.

[wing328]

@Ikelio thanks for the PR. Can we add the test spec mentioned in the issue to the csharp test spec so that we've this case covered moving forward?

"schema": {
  "oneOf": [
	{
	"title": "firstEnum",
	"enum": [
		"one",
		"two"
	  ]
	},
	{
	"title": "secondEnum",
	"type": "integer",
	"enum": [
		"0",
		"1"
	]
	}
  ]
}

[Ikelio]

@wing328 yes, where should I do that ?

[C0DK]

can we bump this?

[wing328]

@Ikelio can you please resolve the merge conflicts when you've time?

[wing328]

@C0DK would you like to sponsor @Ikelio to give this PR a higher priority?

[wing328]

@Ikelio I tested with the latest master and can no longer repeat the issue (code compiles)

Can you please test with v7.0.1 to see if this fix is still needed? Thanks.