linux-capture: Lookup session handle without typechecks

g_variant_lookup() obligatorily receives the type of the variant to
lookup. This function is used when retrieving the session handle
from the portal's response, and the variant type passed is "s" (a
string).

However, xdg-desktop-portal had a bug: the documentation explicitly
mentions that the session handle is an object path (of variant type
"o"), but it passed a string (of variant type "s"). This mismatch
was fixed in the xdg-desktop-portal release 1.10 [1], but that broke
the PipeWire capture code, which was passing specifically the "s"
value to the variant lookup.

Fix this by not checking the variant type at all. Object paths ("o")
are simply strings with a few extra checks, and we don't actually need
to perform these checks.

This change probably broke other apps, and that makes me extremely sad :(

[1] https://github.com/flatpak/xdg-desktop-portal/pull/609

plugins/linux-capture/pipewire.c

@@ -958,6 +958,7 @@ static void on_create_session_response_received_cb(
 	UNUSED_PARAMETER(interface_name);
 	UNUSED_PARAMETER(signal_name);
 
+	g_autoptr(GVariant) session_handle_variant = NULL;
 	g_autoptr(GVariant) result = NULL;
 	struct dbus_call_data *call = user_data;
 	obs_pipewire_data *obs_pw = call->obs_pw;
@@ -975,8 +976,10 @@ static void on_create_session_response_received_cb(
 
 	blog(LOG_INFO, "[pipewire] screencast session created");
 
-	g_variant_lookup(result, "session_handle", "s",
-			 &obs_pw->session_handle);
+	session_handle_variant =
+		g_variant_lookup_value(result, "session_handle", NULL);
+	obs_pw->session_handle =
+		g_variant_dup_string(session_handle_variant, NULL);
 
 	select_source(obs_pw);
 }