Update modus-themes to their latest version

Update modus-themes to their latest version

* admin/MAINTAINERS: Update link to the Git repository of the
modus-themes; point to the new mailing list; include command for
sending a bug report.

* doc/misc/modus-themes.org (Install from the archives): Minor
rewording.
(Dealing with byte compilation errors): Clarify that occasional bugs
are not always a fault of the themes.
(Custom hl-todo colors): Add note about package.:(Full support for
packages or face groups, Indirectly covered packages): Update lists of
supported packages.
(Note on avy hints): Remove obsolete node.
(Note on git-gutter in Doom Emacs): Note problem with custom bitmaps,
which is not the fault of the themes.
(Note on display-fill-column-indicator-mode): Show how to use a
thicker indicator.:(Why are colors mostly variants of blue, magenta,
cyan?): Minor rewording.
(Sources of the themes): Update official theme sources.
(Issues you can help with)
(Patches require copyright assignment to the FSF): Update the
information on potential contributions.
(Acknowledgements): Update list of contributors in the form of code or
ideas/feedback.
(Meta, Other notes about the project): Rename section and include more
links to development-related blog posts.

* etc/themes/modus-themes.el (seq): Stop requiring 'seq'.
(modus-themes--version): Use internal variable for the themes'
version.
(modus-themes-operandi-colors, modus-themes-vivendi-colors): Make
minor tweaks to the color palettes.
(modus-themes-variable-pitch): Remove obsolete symbol from doc string.
(modus-themes--alist-or-seq): Update function to not rely on 'seq'.
(modus-themes--current-theme): Make stylistic tweaks.
(modus-themes--markup): Use correct order of inheritance for faces.
(modus-themes--paren, modus-themes--heading)
(modus-themes--agenda-structure, modus-themes--agenda-date)
(modus-themes--agenda-habit, modus-themes--mode-line-attrs)
(modus-themes--mode-line-padded-box, modus-themes--button): Update to
use 'modus-themes--property-lookup' instead of the previous function
that depended on 'seq'.
(modus-themes--diff): Make it combine as expected with the user option
'modus-themes-deuteranopia'.
(modus-themes-faces): Update list of faces.
(modus-themes-custom-variables): Expand support for face rotation in
'highlight-changes'.

* etc/themes/modus-operandi-theme.el:
* etc/themes/modus-vivendi-theme.el: Bump version number to 2.4.1.

Release notes: <https://protesilaos.com/codelog/2022-06-01-modus-themes-2-4-0/>.