glib.supp: Tweak reachable allocation suppressions

Suppress the cached charset from `g_get_charset()`, and widen the
suppression of the global random number `GRand` instance, since it can
be used outside test cases.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

Fixes: #2134

glib.supp

@@ -218,7 +218,7 @@
 }
 
 {
-	g-test-rand-init2
+	g-rand-init2
 	Memcheck:Leak
 	match-leak-kinds:reachable
 	fun:calloc
@@ -226,8 +226,6 @@
 	fun:g_rand_new_with_seed_array
 	...
 	fun:get_global_random
-	...
-	fun:g_test_init
 }
 
 {
@@ -967,3 +965,13 @@
 	...
 	fun:g_file_*
 }
+
+# Cached charset
+{
+	g_get_charset
+	Memcheck:Leak
+	match-leak-kinds:reachable
+	fun:malloc
+	...
+	fun:g_get_charset
+}