fix: enum generation if it does contain only equality-sign

[dswistowski]

in case of type like:

CREATE TYPE operator AS ENUM ( '=', '>', '<', '>=', '<=' ); 

current plugin will generate wrong python code:

class Operator(str, enum.Enum): = "=" = ">" = "<" = ">=" = "<=" 

after this change plugin will generate valid enum:

class Operator(str, enum.Enum): EQ = "=" GT = ">" LT = "<" GTEQ = ">=" LTEQ = "<="