Specify yarn 1.22.22 in .tool-versions

PR #6612 added yarn to .tool-versions instead of specifying that it
should be installed using homebrew. The version you get when installing
using homebrew is 1.22.22[1] ("Yarn classic") while the version added to
.tool-versions was 4.9.4 ("Yarn modern"). I've opened a draft PR[2] to
follow the migration guide to upgrade to Yarn modern but it seems like
it might be a bit involved. In the meantime all the developers will
start to see changes to .package.json and the addition of new yarn
related files when they run `yarn install`. I think it's safer for now
to retain the behaviour prior to #6612 while we work on #6681 in the
background.

[1]: https://formulae.brew.sh/formula/yarn
[2]: #6681

Author: chrisroos

.tool-versions

@@ -7,5 +7,5 @@ python     3.14.4
 ruby       4.0.3
 shellcheck 0.11.0
 yamllint   1.38.0
-yarn       4.9.4
+yarn       1.22.22
 uv         0.11.7