make collection xref for git help

main.rkt

@@ -123,9 +123,10 @@
                   (lambda ()
                     (error 'git-help "unknown help topic: ~a" topic)))
         'git))
-  ;; Use Racket's installed-documentation cross-reference database instead of
-  ;; guessing where raco setup placed this package's generated HTML.
-  (define xref (load-collections-xref))
+  ;; Build a fresh installed-documentation cross-reference database instead of
+  ;; using load-collections-xref's process-local cache. This makes help notice
+  ;; documentation generated by raco setup during the current DrRacket session.
+  (define xref (make-collections-xref))
   (define tag
     (xref-binding->definition-tag xref (list 'git binding) #f))
   (unless tag