Omit source/build file snapshots from set-version script tests

Summary:
Make the snapshot output of this test terser (since `set-version` is a superset of the fully tested `set-rn-version` script). Notably, this removes any instances of `generated` from the snapshot file, which would hide the diff in PRs.

Changelog: [Internal]

Reviewed By: lunaleaps

Differential Revision: D54420338

fbshipit-source-id: e4a94b1fda34efaedf1b309496954be35acd5f98

Author: huntie