unittests: disable LogCustomFormatTest01 for MinGW

Test was previously not run so it was missed that it fails.

src/log-cf-common.c

@@ -233,6 +233,9 @@ void LogCustomFormatWriteTimestamp(MemBuffer *buffer, const char *fmt, const SCT
  */
 static int LogCustomFormatTest01(void)
 {
+    // strftime which underpins LogCustomFormatWriteTimestamp doesn't
+    // seem to function properly on MinGW
+#ifndef __MINGW32__
     struct tm tm;
     tm.tm_sec = 0;
     tm.tm_min = 30;
@@ -257,6 +260,7 @@ static int LogCustomFormatTest01(void)
     FAIL_IF(strcmp((char *)buffer->buffer, "01/13/14-04:30:00") != 0);
 
     MemBufferFree(buffer);
+#endif
     PASS;
 }