Add release-notes/5.26.1.md

#1681 - Copy-edits on MySQL version notices

* The titles for PHP+MySQL notices should use the same
  capitalization/hyphenation ("Out-of-Date" vs "Out of date").
* Extract some more "%n" variables. Fix one errant variable.
* Reduce floweriness of the "version" / "at least" / "or later" text.
* Make it possible to add/remove the "+" notation without changing
  the ts() message.

[REF] Start to convert Dummy processor to use PropertyBag

Payment PropertyBag - Fix setAmount

#1681 Add in notice about 5.28 Dropping MySQL 5.5 Support

[REF] Remove always NULL param modified_id

#1797 Fix jquery Credit card validation on front end contribu…

Add MembershipType to Api4

Convert remaining Authorize.net test to use guzzle

set boolean fields to false if not set.

[Ref] remove calls to, and deprecate, pending function

Make reCAPTCHA settings clearer

[NFC] Fix use of single quotes, strict operator

Test fixes to support apiv4 add of MembershipType

dev/core/-/issues/1794, changed int to tinyint for boolean fields

This funnction is not now shared with any other forms

This allows us to remove the handling for when a.net doesn't reply

5.26

5.26.0 - Small edits

5.26

5.26.0 release notes final

APIv4 - Support pseudoconstant suffixes in orderBy clause

[REF] Extract createFollowUpActivities

5.26