Strengthen Unicode variable test assertion

Assert that the CSS vars export block contains the decoded
property name (--quarto-scss-export-présentation-bg), not just
that the SCSS compiled successfully.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: cderv

tests/docs/smoke-all/2026/02/20/issue-14065-var.qmd

@@ -9,7 +9,7 @@ _quarto:
   tests:
     html:
       ensureCssRegexMatches:
-        - ['#test-unicode-var', 'background-color']
+        - ['#test-unicode-var', '--quarto-scss-export-pr.*sentation-bg']
 ---
 
 Content with a unicode-named color variable in SCSS.