Ensure README changes don't affect whitespace (#296)

Co-authored-by: Hugo van Kemenade <[email protected]>

Author: AA-Turner

release.py

@@ -466,9 +466,9 @@ def tweak_readme(tag: Tag, filename: str = "README.rst") -> None:
     print(f"Updating {filename}...", end=" ")
     readme = Path(filename)
 
-    # Update first line: "This is Python version 3.14.0 alpha 7"
+    # Update first line: "This is Python version X.Y.Z {release_level} N"
     # and update length of underline in second line to match.
-    lines = readme.read_text().splitlines()
+    lines = readme.read_text().split("\n")
     this_is = f"This is Python version {tag.long_name}"
     underline = "=" * len(this_is)
     lines[0] = this_is

tests/test_release.py

@@ -110,8 +110,11 @@ def test_tweak_readme(
     release.tweak_readme(tag, filename=str(readme_file))
 
     # Assert
-    original_lines = original_contents.splitlines()
-    new_lines = readme_file.read_text().splitlines()
+    original_lines = original_contents.split("\n")
+    new_contents = readme_file.read_text()
+    new_lines = new_contents.split("\n")
     assert new_lines[0] == expected_version
     assert new_lines[1] == expected_underline
     assert new_lines[2:] == original_lines[2:]
+    assert original_contents.endswith("\n")
+    assert new_contents.endswith("\n")