fix(spa): remove trailing whitespace in spa.html

Remove trailing whitespace from the style block to comply with pre-commit hooks.

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

Author: eschutho

superset/templates/superset/spa.html

@@ -35,7 +35,7 @@
         background: #fff;
         color: #000;
       }
-    
+
       @media (prefers-color-scheme: dark) {
         body {
           background: #000;