debian: Add flash-image deps as build-deps

This ensure help2man can work

debian/control

@@ -6,6 +6,11 @@ Build-Depends:
  debhelper (>= 11),
  flake8,
  help2man,
+ python3-coloredlogs,
+ python3-jenkins,
+ python3-requests,
+ python3-tqdm,
+ python3-yaml,
  shellcheck,
 Standards-Version: 4.1.3
 Homepage: https://source.puri.sm/Librem5/librem5-devkit-tools/