New garage; the garage door lights go on every time you cross the beam, the outlets that power up the garage door lights are GFCI protected. Can I use the test button as a disconnect during the daytime hours on a daily basis?
A GFCI needs to be labeled as a disconnecting means to be used as one
A normal receptacle or deadfront GFCI is not labeled or listed for disconnecting use -- it won't kill you for abusing it that way, but it could lead to some premature wear on the GFCI's contacts, shortening its lifespan.
There are deadfront GFCIs that are listed and labeled for this task, but they are uncommon, and will have "ON" and "OFF" labeled on/near the buttons in addition to "RESET" and "TEST", as depicted below:
GFCI breakers are a different story though
However, a breaker-type GFCI is also a perfectly cromulent circuit breaker, and thus is considered a disconnecting means under the NEC even if it is not listed/labeled for SWD (Switching Duty) service. (I know of no circumstance under the NEC where an appropriately rated circuit breaker, whether SWD listed/labeled or not, is not a legal disconnecting means.)
Yes, if the GFCI is designed for that use, and listed for that use. I was forced to amend this answer when I discovered one that actually was!