Add an empty mathematics topic to test the topics list.

Would love to get my paws on the XML export of emaths.education !

01.courses/00.mathematics/frontmatter.yaml

+# This page configuration is shared by all locales, in this directory.
+# You can override it in the individual frontmatter of the pages.
+
+content:
+    # https://learn.getgrav.org/15/content/collections#summary-of-collection-options
+    items: @self.children
+
+anchors:
+    active: false
\ No newline at end of file

01.courses/00.mathematics/topic.en.md

+---
+title: Mathematics
+slug: mathematics
+---
\ No newline at end of file

01.courses/frontmatter.yaml

@@ -4,3 +4,6 @@
 content:
     # https://learn.getgrav.org/15/content/collections#summary-of-collection-options
     items: @self.children
+
+anchors:
+    active: false
\ No newline at end of file