Fix temp-dir path in submodule tests for Windows.

The function make-temporary-file supplies a string
argument consisting of digits to the format function.
Therefore, if the template uses the ~s formatting
escape, make-temporary-file will attempt to create
a temporary directory with double quotes in the path.
Such paths are now allowed on Windows.

pkgs/racket-test-core/tests/racket/submodule.rktl

@@ -636,7 +636,7 @@
 ;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;; Directory for testing
 
-(define temp-dir (make-temporary-file "submodule-tests-~s" 'directory))
+(define temp-dir (make-temporary-file "submodule-tests-~a" 'directory))
 
 ;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;; Check submodule resolution of relative paths: