prep for 4.2.0 and fix changelog (#10375)

something weird happened to the changelog in
https://github.com/certbot/certbot/pull/10319. a 4.2.0 entry was added
below the entry for `5.0.0 - main` despite 4.2.0 not having been
released. since it's sounding like we're expecting our next release to
be 4.2.0 and not 5.0, i merged these two changelog entries into one for
4.2.0

i also modified our setup.py files to use 4.2.0.dev0 instead of
5.0.0.dev0 altho this isn't strictly necessary because our release
script will automatically set all version numbers to whatever version we
give it on the command line before building the release

certbot/CHANGELOG.md

@@ -2,11 +2,11 @@
 
 Certbot adheres to [Semantic Versioning](https://semver.org/).
 
-## 5.0.0 - main
+## 4.2.0 - main
 
 ### Added
 
-*
+* Added `--eab-hmac-alg` parameter to support custom HMAC algorithm for External Account Binding.
 
 ### Changed
 
@@ -25,12 +25,6 @@ Certbot adheres to [Semantic Versioning](https://semver.org/).
 
 More details about these changes can be found on our GitHub repo.
 
-## 4.2.0
-
-### Added
-
-* Added `--eab-hmac-alg` parameter to support custom HMAC algorithm for External Account Binding.
-
 ## 4.1.1 - 2025-06-12
 
 ### Fixed

certbot/src/certbot/__init__.py

@@ -1,4 +1,4 @@
 """Certbot client."""
 
 # version number like 1.2.3a0, must have at least 2 parts, like 1.2
-__version__ = '5.0.0.dev0'
+__version__ = '4.2.0.dev0'