So apparently the method Mautrix bridges instructs to use to install git head using pip is deprecated and will be phased out at some point. Needs probably changing to whatever the command suggests, I'd assume.
(mautrix-telegram) mautrix-telegram@morpheus:~/mautrix-telegram$ pip install --upgrade git+https://github.com/mautrix/telegram.git#egg=mautrix-telegram[all]
DEPRECATION: git+https://github.com/mautrix/telegram.git#egg=mautrix-telegram[all] contains an egg fragment with a non-PEP 508 name pip 25.0 will enforce this behaviour change. A possible replacement is to use the req @ url syntax, and remove the egg fragment. Discussion can be found at https://github.com/pypa/pip/issues/11617
So apparently the method Mautrix bridges instructs to use to install git head using pip is deprecated and will be phased out at some point. Needs probably changing to whatever the command suggests, I'd assume.