Use master;

Create User TestNonSA Without login With default_schema = dbo;
Go

Grant Create Procedure to TestNonSA;
Grant Alter on schema::dbo to TestNonSA;
Go

Execute As User = 'TestNonSA';
Go

Create Procedure dbo.Test1
As
Select 1 As TestAnswer
Go

Revert
Go

Drop User TestNonSA;
Drop Procedure dbo.Test1;