Fix file menu separator

[HebaruSan]

Problem

There's supposed to be a separator line between Audit recommendations and Exit, but it doesn't appear:

Cause

Wanting to be frugal, I re-used toolStripSeparator3 rather than creating a new separator, since the actual separator object stores essentially no data.

That apparently doesn't work.

Changes

Now we use a new toolStripSeparator7 object instead. This makes the separator show up: