Windows test runner: show process name instead of test name

If a test failed we would previously see:

  Output from process `test_foo`: blah
  Output from process `test_foo`: (nothing)

This commit changes it to:

  Output from process `test_foo`: blah
  Output from process `foo_helper`: (nothing)

test/runner-win.c

@@ -135,7 +135,7 @@ int process_start(char *name, char *part, process_info_t *p) {
   p->stdio_in = nul;
   p->stdio_out = file;
   p->process = pi.hProcess;
-  p->name = name;
+  p->name = part;
 
   return 0;