Conformance - fix saving toml results file in non-unicode

Noticed that pyright is giving unicode output that on Windows is leading to issues generating reports later. Saving this output explicitly as unicode resolves the issue.

```python
Generating summary report
Traceback (most recent call last):
  File "\typing\conformance\src\main.py", line 260, in <module>
    main()
  File "\typing\conformance\src\main.py", line 256, in main
    generate_summary(root_dir)
  File "\typing\conformance\src\reporting.py", line 19, in generate_summary
    summary = template.replace("{{summary}}", generate_summary_html(root_dir))
                                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "\typing\conformance\src\reporting.py", line 87, in generate_summary_html
    results = tomli.load(f)
              ^^^^^^^^^^^^^
  File "src\tomli\_parser.py", line 134, in load
UnicodeDecodeError: 'utf-8' codec can't decode byte 0xa0 in position 110: invalid start byte
```

Author: Andrej730

conformance/src/main.py

@@ -197,7 +197,7 @@ def update_output_for_test(
                 notes = "\n" + notes
             existing_results["notes"] = tomlkit.string(notes, multiline=True)
         results_file.parent.mkdir(parents=True, exist_ok=True)
-        with open(results_file, "w") as f:
+        with open(results_file, "w", encoding="utf-8") as f:
             tomlkit.dump(existing_results, f)