[Backport 13.4] fix: remove superfluous backslash in foreign_field co…

…nfval title (#1199)

fix: remove superfluous backslash in foreign_field confval title

Co-authored-by: Chris Müller <2566282+brotkrueml@users.noreply.github.com>

Documentation/ColumnsConfig/Type/Inline/_Properties/_ForeignField.rst.txt

@@ -1,6 +1,6 @@
 ..  _columns-inline-properties-foreign-field:
 
-..  confval:: foreign\_field
+..  confval:: foreign_field
     :name: inline-foreign-field
     :Path: $GLOBALS['TCA'][$table]['columns'][$field]['config']
     :type: string