REMOVE ME: Temporarily run riscv64gc in PR

Author: Hoverbear

src/ci/docker/host-x86_64/disabled/riscv64gc-gnu/Dockerfile renamed to src/ci/docker/host-x86_64/riscv64gc-gnu/Dockerfile

@@ -92,6 +92,9 @@ pr:
   - image: x86_64-gnu-tools
     <<: *job-linux-16c
 
+  - image: dist-riscv64-linux
+    <<: *job-linux-4c
+
 # Jobs that run when you perform a try build (@bors try)
 # These jobs automatically inherit envs.try, to avoid repeating
 # it in each job definition.