patch 8.2.4764: CI uses an older gcc version

Problem:    CI uses an older gcc version.
Solution:   Use GCC 11. (closes #10185)
diff --git a/src/testdir/lsan-suppress.txt b/src/testdir/lsan-suppress.txt
index ec999fa..c0d9061 100644
--- a/src/testdir/lsan-suppress.txt
+++ b/src/testdir/lsan-suppress.txt
@@ -1,4 +1,4 @@
-# Suppress leaks from X libraries on Ubuntu bionic.
+# Suppress leaks from X libraries on Ubuntu focal.
 leak:libX11.so.6
 leak:libXt.so.6
 leak:libcairo.so.2