font: disable sprite test in valgrind

src/font/sprite/Face.zig

@@ -511,6 +511,9 @@ fn testDrawRanges(
 }
 
 test "sprite face render all sprites" {
+    // This test is way too slow to run under Valgrind, unfortunately.
+    if (std.valgrind.runningOnValgrind() > 0) return error.SkipZigTest;
+
     // Renders all sprites to an atlas and compares
     // it to a ground truth for regression testing.
 

valgrind.supp

@@ -574,6 +574,18 @@
    ...
 }
 
+{
+   pango language
+   Memcheck:Leak
+   match-leak-kinds: possible
+   fun:calloc
+   fun:g_malloc0
+   fun:pango_language_from_string
+   fun:pango_language_get_default
+   fun:gtk_get_locale_direction
+   fun:gtk_init_check
+   ...
+}
 {
    Adwaita Stylesheet Load
    Memcheck:Leak