Bump ubuntu from e4771b7 to eb1392b in /dev/ci/docker_linux

Bumps ubuntu from `e4771b7` to `eb1392b`.

---
updated-dependencies:
- dependency-name: ubuntu
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

dev/ci/docker_linux/Dockerfile

@@ -12,7 +12,7 @@
 
 # Last manual update 2021-09-24 (changing this comment will re-build image)
 
-FROM ubuntu:bionic@sha256:eb1392bbdde63147bc2b4ff1a4053dcfe6d15e4dfd3cce29e9b9f52a4f88bc74
+FROM ubuntu:bionic@sha256:c1d0baf2425ecef88a2f0c3543ec43690dc16cc80d3c4e593bb95e4f45390e45
 MAINTAINER Flutter Developers <[email protected]>
 
 RUN apt-get update -y && \