silence misleading warnings about failure to load gvfs modules

The pressure-vessel-wrap binaries shipped in SteamLinuxRuntime containers come with a bundled copy of GLib, taken from SteamRT 1 'scout'. This results in warnings that are completely harmless, but look more serious than they really are:

/usr/lib/gvfs/libgvfscommon.so: undefined symbol: g_task_new
Failed to load module: /usr/lib/gio/modules/libgvfsdbus.so
/usr/lib/gvfs/libgvfscommon.so: undefined symbol: g_task_new
Failed to load module: /usr/lib/gio/modules/libgvfsdbus.so

or

/usr/lib/x86_64-linux-gnu/gio/modules/libdconfsettings.so: undefined symbol: g_type_ensure
Failed to load module: /usr/lib/x86_64-linux-gnu/gio/modules/libdconfsettings.so

These are unimportant, but because they look important, they distract users who are reporting genuine issues, making triaging and debugging more time-consuming.

Despite this only being a cosmetic problem, I think it's low-hanging fruit to fix in a future update, so that people reporting unrelated issues don't get misled. Assigning to myself because I've already done some looking into how this works, and writing patches will be quicker and more precise than explaining it to someone else.

/cc @denittis