Schema typo in server-variable for OpenAPI 3.1.0

[samdbmg]

I think there's a typo in the schema used for validating OpenAPI 3.1.0 specifications.

openapi-spec-validator/openapi_spec_validator/resources/schemas/v3.1/schema.json

Lines 192 to 194 in 91f5cf2

	"descriptions": {
	"type": "string"
	}

Based on https://github.com/OAI/OpenAPI-Specification/blob/main/versions/3.1.0.md#server-variable-object this should be "description" instead of "descriptions" - I imagine the extra s is a typo when it was originally added.

I'll open a PR now.