[PyROOT] Whitelist libgcc_s library in imported library test

On some platforms, the low-level runtime library provided by GCC will
also be loaded when importing ROOT. Therefore, it needs to be added to
the whitelist such that the ROOT Python module tests don't fail because
of it.

Fixes a test failure that I saw on my workstation with NixOS.

bindings/pyroot/pythonizations/test/import_load_libs.py

@@ -70,6 +70,7 @@ class ImportLoadLibs(unittest.TestCase):
             'libnss_.*',
             'ld.*',
             'libffi',
+            'libgcc_s',
             # AddressSanitizer runtime and ROOT configuration
             'libclang_rt.asan-.*',
             'libROOTSanitizerConfig',