Agent targeting rules that have the value 'false' seem to be discarded

So I hit this when importing meta-data tags from GCP. I wanted to target non-preemptible instances, which ends up being `gcp:preemptible=false`. This value showed up in the agent attributes, but the targeting rule was being discarded by the time my job was getting triggered (when I looked on the 'timeline', that clause of the targeting rules wasn't there, while the other ones were).

I was on v3.14, but I upgraded to v3.22 and confirmed the problem is still there. It's easy enough to work around, but was definitely confusing.

P.S. I often miss Github notifications so I might not see your reply. Feel free to close this without me, e.g. in case I'm wrong :)

Start by reproducing the targeting rule with the GCP attribute `gcp:preemptible=false`, then trace where agent attributes or targeting rules are parsed and filtered. Done means the `false` clause remains present when the job is triggered and is visible on the timeline, with a regression test covering this value.

Written by the indexing model from the issue text.