chore: avoid building contracts when producing gates report (#7136)

This build target can be built from `+build-protocol-circuits` rather
than `+build` as it doesn't need access to the contracts in order to do
its job. This will make it complete much faster.

noir-projects/Earthfile

@@ -77,7 +77,7 @@ format:
   RUN nargo fmt --check
 
 gates-report:
-  FROM +build
+  FROM +build-protocol-circuits
   WORKDIR /usr/src/noir-projects
 
   COPY ./gates_report.sh ./gates_report.sh