Fix wrong assignment (#1550)

Assign "PAGE" instead of "10" here.

Co-authored-by: Ralf Merz <mail@merzilla.de>

Author: github-actions[bot]

Documentation/Guide/Page/_fluid-template.typoscript

@@ -1,4 +1,4 @@
-page = 10
+page = PAGE
 page {
   10 = PAGEVIEW
   10 {