Update the modus-themes to their 2.6.0 version

Update the modus-themes to their 2.6.0 version

* doc/misc/modus-themes.org (Sample configuration with and without
use-package): Add missing parenthesis to the manual.
(Option for completion framework aesthetics)
(Custom Org emphasis faces): Minor rewording.
(Custom hl-todo colors): Add instructions on how to add user-level
support for the 'solaire' package, as the modus-themes no longer
support it.
(Full support for packages or face groups): Remove 'solaire' from the
list of supported packages.
(Note on git-gutter in Doom Emacs)
(Note on php-mode multiline comments)
(Note on highlight-parentheses.el): Clarify need to re-load the
theme for changes to take effect.
(Acknowledgements): Update acknowledgements.

* etc/themes/modus-themes.el (modus-themes-faces): Fix typo.
(modus-themes--version): Reword docstring and update to current value.
(modus-themes--weight): Stop using deprecated alias of symbol.

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

Detailed release notes:
<https://protesilaos.com/codelog/2022-08-19-modus-themes-2-6-0/>.