chore: set nullable-type-sibling to warn in minimal ruleset

Author: tatomyr

docs/@v2/rules/minimal.md

@@ -11,7 +11,6 @@ Errors:
 - [no-server-trailing-slash](./oas/no-server-trailing-slash.md)
 - [no-server-variables-empty-enum](./oas/no-server-variables-empty-enum.md)
 - [no-unresolved-refs](./oas/no-unresolved-refs.md)
-- [nullable-type-sibling](./oas/nullable-type-sibling.md)
 - [struct](./oas/struct.md)
 - [stepId-unique](./arazzo/stepId-unique.md)
 - [workflowId-unique](./arazzo/workflowId-unique.md)
@@ -29,6 +28,7 @@ Warnings:
 - [no-server-example.com](./oas/no-server-example-com.md)
 - [no-undefined-server-variable](./oas/no-undefined-server-variable.md)
 - [no-unused-components](./oas/no-unused-components.md)
+- [nullable-type-sibling](./oas/nullable-type-sibling.md)
 - [operation-2xx-response](./oas/operation-2xx-response.md)
 - [operation-operationId-unique](./oas/operation-operationId-unique.md)
 - [operation-operationId-url-safe](./oas/operation-operationId-url-safe.md)

docs/@v2/rules/ruleset-templates.md

@@ -106,7 +106,7 @@ rules:
   operation-singular-tag: off
   no-unresolved-refs: error
   no-enum-type-mismatch: warn
-  nullable-type-sibling: error
+  nullable-type-sibling: warn
   paths-kebab-case: off
   struct: error
   spec-strict-refs: off
@@ -379,6 +379,7 @@ rules:
   operation-singular-tag: off
   no-unresolved-refs: error
   no-enum-type-mismatch: error
+  nullable-type-sibling: error
   paths-kebab-case: off
   struct: error
   spec-strict-refs: off

packages/core/src/config/minimal.ts

@@ -79,7 +79,7 @@ const minimal: RawGovernanceConfig<'built-in'> = {
     'no-unused-components': 'warn',
     'no-undefined-server-variable': 'warn',
     'no-server-variables-empty-enum': 'error',
-    'nullable-type-sibling': 'error',
+    'nullable-type-sibling': 'warn',
     'operation-summary': 'warn',
     'operation-operationId': 'warn',
     'operation-operationId-unique': 'warn',