Automapping stops working when a project's rules.txt is modified during runtime.

**Describe the bug**
My project will occasionally prevent me from using Automap. Restarting Tiled does not work, nor does closing or reopening maps. The only fix for this is going to Project Properties and pointing the Automapping rules to the same file and saving it. Then, automapping works again.

**To Reproduce**

**Expected behavior**
I can apply Automapping by using Ctrl+M or going to Map->Automap.

**Specifications:**
- OS: Win11
- Tiled Version: 1.10.2

Start by reproducing the Automapping failure described for Tiled 1.10.2 on Windows 11: modify the project's rules.txt during runtime, then try Ctrl+M or Map->Automap. Compare this with reselecting the same rules file in Project Properties and saving. Done means Automapping continues to work after the rules file is modified without needing to reselect it.

Written by the indexing model from the issue text.