shell32/tests: Write-strings warnings fix

[Andrew Talbot]

Changelog:
    shell32/tests: Write-strings warnings fix.

diff -urN a/dlls/shell32/tests/shlexec.c b/dlls/shell32/tests/shlexec.c
--- a/dlls/shell32/tests/shlexec.c	2006-05-23 13:48:42.000000000 +0100
+++ b/dlls/shell32/tests/shlexec.c	2006-07-22 18:56:52.000000000 +0100
@@ -475,8 +475,8 @@
 
 typedef struct
 {
-    char* verb;
-    char* basename;
+    const char* verb;
+    const char* basename;
     int rc;
     int todo;
 } filename_tests_t;