doc: typos in file/gif and file/unzip contracts

- missing `for-label` in `file/gif`
- typo in `file/unzip`

pkgs/racket-doc/file/scribblings/gif.scrbl

@@ -1,5 +1,5 @@
 #lang scribble/doc
-@(require scribble/manual
+@(require "common.rkt"
           scribble/extract
           (for-label file/gif))
 

pkgs/racket-doc/file/scribblings/unzip.scrbl

@@ -165,7 +165,7 @@ If @racket[entry] is not in @racket[zipdir], an
          #:changed "6.0.1.12" @elem{Added the @racket[#:utc-timestamps?] argument.}]}
 
 
-@defproc[(call-with-unzip-entry [in path-string? input-port]
+@defproc[(call-with-unzip-entry [in (or/c path-string? input-port?)]
                                 [entry path-string?]
                                 [proc (-> path-string? any)])
          any]{