pidgin/pidgin

Use g_signal_connect_object for PidginProtocolStore to follow the life cycle of the objects and avoid memory errors.

Testing Done:
Ran locally in valgrind.

Before this patch, valgrind noticed `118 errors from 18 contexts` after this patch `14 errors from 5 contexts`.

Reviewed at https://reviews.imfreedom.org/r/458/
---
id: im.pidgin.Finch3
runtime: org.gnome.Platform
runtime-version: '3.36'
sdk: org.gnome.Sdk
command: finch3
finish-args:
- --share=ipc
- --socket=x11
- --share=network
- --talk-name=org.freedesktop.Notifications
- --system-talk-name=org.freedesktop.Avahi
modules:
- packaging/flatpak/libpurple-common.yml
- packaging/flatpak/libgnt.yml
- name: finch3
buildsystem: meson
config-opts:
- -Dgtkui=false
- -Ddoc=false
sources:
- type: dir
path: '.'