Project file remains dirty in Solution Explorer after choosing to not save changes

**Visual Studio Version**: master

**Summary**:

The dirty state of the project file isn't being reset when you close and don't save changes.

**Steps to Reproduce**:

1. Open the project file editor

2. Make some changes

3. Close the tab, and select `No` on the prompt

**Expected Behavior**:
File does not appear modified in solution explorer and git window (if using source control). When reopening the editor the tab doesn't have an asterisk in it.

**Actual Behavior**:
The opposite of above.

**User Impact**:
Minor annoyance and uncertainty.