Fix URL in example_filepath function

- Modified the URL in `example_filepath` function within `bgen_reader/_example.py`
- Updated URL format from `github.com/.../blob` to `raw.githubusercontent.com/...`

This change ensures that the URL correctly points to the raw content of the file
rather than the GitHub page, which allows direct file retrieval for the function.

bgen_reader/_example.py

@@ -18,7 +18,7 @@
 def example_filepath(filename: str):
     import requests
 
-    url = "https://github.com/fastlmm/bgen-sample-files/blob/main"
+    url = "https://raw.githubusercontent.com/fastlmm/bgen-sample-files/main"
 
     if filename not in _filenames:
         raise ValueError(f"Unknown filename {filename}.")