switch to runner use

.github/minimal-runner-image/Dockerfile

@@ -4,9 +4,9 @@ RUN apt -yq update && \
     apt -yq install --no-install-recommends git curl wget ca-certificates
 
 RUN groupadd -g 1000 ubuntu && useradd -ms /bin/bash -u 1000 -g 1000 ubuntu && \
-    groupadd -g 1001 buildifier && useradd -ms /bin/bash -u 1001 -g 1001 buildifier && \
+    groupadd -g 1001 runner && useradd -ms /bin/bash -u 1001 -g 1001 runner && \
     echo "ALL ALL=(ALL) NOPASSWD: ALL" >> /etc/sudoers
 
-USER ubuntu
+USER runner
 
 CMD ["/bin/bash"]