docs: schema regex fix

Co-authored-by: Ralf Handl <ralf.handl@sap.com>

Author: baywet

src/schemas/validation/schema.yaml

@@ -236,7 +236,7 @@ $defs:
           $ref: '#/$defs/operation'
         propertyNames:
           $comment: RFC9110 restricts methods to "1*tchar" in ABNF
-          pattern: "^[a-zA-Z0-9!#$%&'*+.^`|~-]+$"
+          pattern: "^[a-zA-Z0-9!#$%&'*+.^_`|~-]+$"
           not:
             enum:
               - GET