Doc: Fix minor error in ePub (pythonGH-100614)

Fix issue reported https://mail.python.org/archives/list/[email protected]/message/KE7OIAO53P4XRC4ZOWPDHA63ZQJCHEC3/

Author: methane

Doc/conf.py

@@ -268,7 +268,7 @@
 ogp_site_name = 'Python documentation'
 ogp_image = '_static/og-image.png'
 ogp_custom_meta_tags = [
-    '<meta property="og:image:width" content="200">',
-    '<meta property="og:image:height" content="200">',
-    '<meta name="theme-color" content="#3776ab">',
+    '<meta property="og:image:width" content="200" />',
+    '<meta property="og:image:height" content="200" />',
+    '<meta name="theme-color" content="#3776ab" />',
 ]