Fix the Dockerfile in case of Kaniko build (#15510)

Kaniko does not support looking up binaries from $PATH, so we
specify the full path to the bash binary.

Co-authored-by: kaiyou <dev@kaiyou.fr>

Dockerfile

@@ -1,7 +1,7 @@
 FROM ubuntu:20.04 as build-dep
 
 # Use bash for the shell
-SHELL ["bash", "-c"]
+SHELL ["/usr/bin/bash", "-c"]
 
 # Install Node v12 (LTS)
 ENV NODE_VER="12.20.0"