fix: remove trailing whitespace from spa.html template

Pre-commit automatically fixed trailing whitespace in the spa.html template file.

🤖 Generated with [Claude Code](https://claude.ai/code)

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;