registry: do not load .so* files or folders
Latest meson is creating a .so.p temporary folder to lua-factory plugin and current code in grl-registry would try to load all .so* files. This patch makes sure that it only tries to load files with .so suffix (actually, G_MODULE_SUFFIX that could be different in other platforms)
Fixes: Bail out! Grilo-FATAL-WARNING: [registry] ../subprojects/grilo/src/grl-registry.c:1210: Failed to open module: /builds/victortoso/grilo-plugins/_build/src/lua-factory/libgrlluafactory.so.p: cannot read file data: Is a directory
Fixed CI in Grilo Plugins here