QA: run ubuntu-only (drop os matrix from the QA group) (#312)

* QA: run ubuntu-only (drop os matrix from the QA group)

Aqua/JET are platform-independent, so the windows/macos QA jobs were
wasted CI. Remove the os axis from the [QA] group in test/test_groups.toml
so QA runs only on the default ubuntu-latest. Core/functional groups keep
their multi-OS coverage.

Co-Authored-By: Chris Rackauckas <accounts@chrisrackauckas.com>
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* QA: normalize versions to [lts, 1] (drop pre)

Set the [QA] group versions to the canonical set ["lts", "1"] so Aqua/JET
run on LTS (1.10) and latest stable only (dropping "pre"). Core and NoPre
groups are unchanged.

Co-Authored-By: Chris Rackauckas <accounts@chrisrackauckas.com>
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Chris Rackauckas (Claude) <accounts@chrisrackauckas.com>
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: 3 people

test/test_groups.toml

@@ -3,8 +3,7 @@ versions = ["1", "lts", "pre"]
 os = ["ubuntu-latest", "macos-latest", "windows-latest"]
 
 [QA]
-versions = ["1", "lts", "pre"]
-os = ["ubuntu-latest", "macos-latest", "windows-latest"]
+versions = ["lts", "1"]
 
 [NoPre]
 versions = ["1", "lts", "pre"]