Update to the latest Serai Substrate (#125)

* Update to the latest Serai Substrate

* Add Protobuf to build dependencies

Docker shouldn't need updating as this should've been added to the image 
in 
2dbace5b01.

* Get substrate to build

* Correct protoc build step

* Remove the benchmarking code

There's some macro resolution error that isn't apparent. I worked on it 
for about half an hour but...

* Remove unnecessary clone

* Correct runtime-benchmarks flag usage

.github/actions/build-dependencies/action.yml

@@ -15,6 +15,9 @@ inputs:
 runs:
   using: "composite"
   steps:
+    - name: Install Protobuf
+      uses: arduino/setup-protoc@v1
+
     - name: Install solc
       shell: bash
       run: |