patch 9.0.0300: 'cpoptions' tests are flaky

Problem:    'cpoptions' tests are flaky.
Solution:   Use a different file name for each test.
diff --git a/src/version.c b/src/version.c
index 1af4b7d..fcd142e 100644
--- a/src/version.c
+++ b/src/version.c
@@ -708,6 +708,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    300,
+/**/
     299,
 /**/
     298,