[plot] Assume a figure can contain multiple axes

For example a twin axis
4 jobs for twin-legend in 8 minutes and 26 seconds (queued for 6 seconds)
Status Job ID Name Coverage
  Build
passed #229829
docker
build_linux_37

00:04:24

80.0%
passed #229830
docker
build_linux_38

00:04:25

81.0%
passed #229827
intel macos
build_macos_intel_37

00:08:25

80.0%
passed #229828
intel macos
build_macos_intel_38

00:08:20

81.0%