ci: modify valgrind suppressions

tests/unit/valgrind.suppressions

@@ -12,7 +12,31 @@
    ...
    fun:main
 }
-
+# Backtrace might generate false positives with its _dl_open function call: https://stackoverflow.com/questions/78525668/egl-memory-leak
+{
+   stacktrace_suppression
+   Memcheck:Leak
+   match-leak-kinds: possible
+   fun:malloc
+   fun:malloc
+   fun:_dlfo_mappings_segment_allocate
+   fun:_dl_find_object_update_1
+   fun:_dl_find_object_update
+   fun:dl_open_worker_begin
+   fun:_dl_catch_exception
+   fun:dl_open_worker
+   fun:_dl_catch_exception
+   fun:_dl_open
+   fun:do_dlopen
+   fun:_dl_catch_exception
+   fun:_dl_catch_error
+   fun:dlerror_run
+   fun:__libc_dlopen_mode
+   fun:__libc_unwind_link_get
+   fun:backtrace
+   ...
+   fun:main
+}
 # TODO: fix the pedantic leak errors from s2n_fork_generation_number_test
 {
    ignore_s2n_fork_generation_number_test