chore(changeset): split solid-query into its own fixed group (#10983)

solid-query is tracking the Solid 1 -> 2 breaking jump and is on a v6
pre-release line, while query-core and the other adapters remain on v5.
Because all of react/core/vue/solid shared a single `fixed` group, the
solid v6 beta changesets dragged every package in that group to
6.0.0-beta.5, even though no changeset targets them.

Carve the three solid packages into their own `fixed` group so they can
version independently on the v6 line. This mirrors the existing svelte
group (already on 6.x while core stays on 5.x) and matches the agreed
policy that version-syncing should happen across majors only -- no v6
beta of unaffected adapters.

Verified with `changeset version` (prerelease mode): only solid-query,
solid-query-devtools and solid-query-persist-client bump to
6.0.0-beta.5; query-core/react-query/vue-query stay at 5.101.0 and
svelte-query stays at 6.1.34.

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

Author: manudeli

.changeset/config.json

@@ -26,10 +26,12 @@
       "@tanstack/react-query-devtools",
       "@tanstack/react-query-next-experimental",
       "@tanstack/react-query-persist-client",
+      "@tanstack/vue-query"
+    ],
+    [
       "@tanstack/solid-query",
       "@tanstack/solid-query-devtools",
-      "@tanstack/solid-query-persist-client",
-      "@tanstack/vue-query"
+      "@tanstack/solid-query-persist-client"
     ],
     [
       "@tanstack/vue-query-devtools",