fix linked axis regression and add unit test

[jkrumbiegel]

Not proliferating the targetlimits update when it got the same limits again broke the linkaxis functionality.

[MakieBot]

Compile Times benchmark

Note, that these numbers may fluctuate on the CI servers, so take them with a grain of salt.

using time

master:  9.24 < 9.27 > 9.40, 0.05+-
pr:      9.23 < 9.26 > 9.41, 0.07+-
speedup: 0.98 < 1.00 > 1.02, 0.01+-
median:  -0.03% => invariant

This PR does not change the using time.

ttfp time

master   24.24 < 24.31 > 24.51, 0.09+-
pr       24.26 < 24.33 > 24.56, 0.11+-
speedup: 0.99 < 1.00 > 1.00, 0.00+-
median:  +0.09% => invariant

This PR does not change the ttfp time.