Temporarily switch to a single build-args argument

[bretthoerner]

The way I had it is definitely the way it works in github/build-push-action, but I guess depot doesn't support this?

I verified in the Depot run that it is putting both args into the same --build-args (which is not what we want):

2024-02-07T15:30:23.6497484Z [command]/opt/hostedtoolcache/depot/2.53.0/arm64/depot build --build-arg RUST_BACKTRACE=1 BIN=hook-worker --cache-from ...

I'll have to bring it up with their support. For now, I'd like to get the build working.

(Additionally, RUST_BACKTRACE=1 came from the capture repo, and it's an argument to the build. Was rustc crashing for capture at some point? Either way, it doesn't seem strictly necessary to have in there this very second, so that I can get unblocked here.)

[xvello]

Indeed, I don't recall why we'd need this for capture. Suspected it was to enable continuous profiling but, that another field in Cargo.toml (that I need to remove btw)