fix: use the constructor function every time a periodic job is scheduled, instead of when its registered

[elee1766]

right now, the constructor gets called when converting to an internal job, which causes the constructor to use the value at add time.

however, the comments say

// The constructor function is invoked each time a periodic job's schedule
// elapses, returning job arguments to insert along with optional insertion
// options.

so im assuming this is whats intended?

[brandur]

Oops, yes, thanks! I'll try to add a test case to verify this.