AddonManager never goes further “Checking connection”

Here `reply` is always `None`, rendering the function useless. That's a known peculiarity of `PySide6`.

https://github.com/FreeCAD/AddonManager/blob/a38c8f003e8131bb7588313374abb4ccb26da9e9/NetworkManager.py#L550

As a workaround against that, I suggest changing
https://github.com/FreeCAD/AddonManager/blob/a38c8f003e8131bb7588313374abb4ccb26da9e9/NetworkManager.py#L256
to
```python
reply.finished.connect(lambda r=reply: self.__reply_finished(r))
```
and
https://github.com/FreeCAD/AddonManager/blob/a38c8f003e8131bb7588313374abb4ccb26da9e9/NetworkManager.py#L547-L550
to
```python
def __reply_finished(self, reply: QtNetwork.QNetworkReply | None = None) -> None:
"""Called when a reply has been completed: this makes sure the data has been read and
any notifications have been called."""
if reply is None:
reply = self.sender()
```
to maintain the compatibility with calls I might've missed. I find the solution dirty, but it works.

There are many more places like this, even in the file. That's the reason I make the issue, not a PR.

---

### FreeCAD Info:

**OS:** Manjaro Linux (KDE/plasma/wayland)
**Architecture:** x86_64
**Version:** 1.0.2.39319 (Git)
**Build type:** Release
**Branch:** `makepkg`
**Hash:** `256fc7eff3379911ab5daf88e10182c509aa8052`
**Python** 3.13.7, Qt 6.10.1, Coin 4.0.5, Vtk 9.5.2, OCC 7.9.2
**Locale:** English/United States (en_US)
**Stylesheet/Theme/QtStyle:** `FreeCAD Dark.qss`/FreeCAD Dark/
**Installed mods:**
* `CADExchanger`
* `fasteners-backup-before-zip-migration` 0.5.33 (Disabled) ← _this proves the changes work well!_
* `fasteners` 0.5.43
* `pcb` 6.2023.1
* `manifest.json`