v2.22.0-rc4

ci: try specific main path to fix notarization (#246)

For as-yet unknown reasons, the macOS notarization step that seems to
have run as part of building
https://github.com/mccutchen/go-httpbin/releases/tag/v2.22.0-rc2 yielded
binaries that macOS refuses to run.

Throwing stuff at the wall here, let's see what this does.