fix: add integer to the list of numeric types

[psteinroe]

What kind of change does this PR introduce?

bug fix

What is the current behavior?

the return type integer of a function is unknown

What is the new behavior?

integer is correctly parsed as number

[soedirgo]

Can you provide a test case for this? I'm not able to reproduce this issue:

postgres=# create function f() returns integer language sql as 'select 1';
CREATE FUNCTION

...
      f: {
        Args: Record<PropertyKey, never>
        Returns: number
      }
...

Note that an integer return type would show up as int4 in this case, they're equivalent: https://www.postgresql.org/docs/current/datatype-numeric.html#DATATYPE-INT