libqcdm,reset: fix warnings with -Wdiscarded-qualifiers

reset.c: In function ‘main’:
  reset.c:238:17: warning: passing argument 1 of ‘putenv’ discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]
    238 |         putenv ("QCDM_DEBUG=1");
        |                 ^~~~~~~~~~~~~~
  In file included from reset.c:22:
  /usr/include/stdlib.h:647:26: note: expected ‘char *’ but argument is of type ‘const char *’
    647 | extern int putenv (char *__string) __THROW __nonnull ((1));
        |                    ~~~~~~^~~~~~~~

libqcdm/tests/reset.c

@@ -235,7 +235,7 @@ main (int argc, char *argv[])
         debug = 1;
 
     if (debug)
-        putenv ("QCDM_DEBUG=1");
+        putenv ((char *)"QCDM_DEBUG=1");
 
     fd = com_setup (dmport);
     if (fd < 0)