patch 8.2.4764: CI uses an older gcc version

Problem:    CI uses an older gcc version.
Solution:   Use GCC 11. (closes #10185)

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

src/version.c

@@ -746,6 +746,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    4764,
 /**/
     4763,
 /**/