patch 9.0.0267: Coverity workflow still uses Ubuntu 18.04

Problem:    Coverity workflow still uses Ubuntu 18.04.
Solution:   Use Ubuntu 20.04
diff --git a/src/version.c b/src/version.c
index 50294f8..b5cdfdf 100644
--- a/src/version.c
+++ b/src/version.c
@@ -728,6 +728,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    267,
+/**/
     266,
 /**/
     265,