[doc] Perldeltas for stable point releases refer to the previous dev rather than stable release

[Grinnz]

Where

perl5361delta and following stable point release deltas

Description

Seemingly since 5.36.1, the perldeltas for stable point release have not followed the right logic for "if you are upgrading from an earlier release such as..." which should refer to the preceding stable version and not the preceding dev version. I can (and may shortly) open a PR to fix this in the existing deltas, but I'm not sure if something can be fixed in the RMG process to get this right, hence this issue.

i.e. in perl5361delta, it says

If you are upgrading from an earlier release such as 5.35.0, first read [perl5360delta](https://perldoc.perl.org/perl5360delta), which describes differences between 5.35.0 and 5.36.0.

where it should refer to 5.34.0. (perl5382delta contains the same error as perl5381delta most likely due to copy paste for that bugfix release, but in general it is just the first point releases with this issue.)

[steve-m-hay]

This didn't start with 5.36.1: 5.34.1 refers to 5.33.0, 5.32.1 refers to 5.31.0 and 5.30.0 refers to 5.29.0.
The last one to get it right was 5.28.1, which refers to 5.26.0.
So this has been wrong since 5.28.1 in Nov 2019 and nobody has noticed until now!
A note in the RMG about it would hopefully stop in happening again. There are similar lines in the INSTALL document which are also tricky to get right, especially in .1 releases, which the RMG already talks about.

[Grinnz]

It looks like a couple of these were previously corrected in #18599