Refactor the untracked files check

Co-Authored-By: Pradyun Gedam <pradyunsg@gmail.com>

noxfile.py

@@ -262,19 +262,28 @@ def build_dists(session):
     session.log(
         "# Check if there's any Git-untracked files before building the wheel",
     )
-    has_git_untracked_files = any(
-        bool(l) for l in
-        # session.run doesn't seem to return any output
-        subprocess.check_output(
-            (
-                "git", "ls-files", "--ignored", "--exclude-standard",
-                "--others", "--", ".",
-            ),
-            text=True,
-        ).split('\n')
-        if not l.startswith('.nox/build-release/')  # exclude nox env file
+
+    def get_git_untracked_files():
+        """List all local file paths that aren't tracked by Git."""
+        git_ls_files_cmd = (
+            "git", "ls-files", "--ignored", "--exclude-standard",
+            "--others", "--", ".",
+        )
+        # session.run doesn't seem to return any output:
+        ls_files_out = subprocess.check_output(git_ls_files_cmd, text=True)
+        ls_files_out_lines = ls_files_out.splitlines()
+        for file_name in ls_files_out_lines:
+            if file_name.strip():  # it's useless if empty
+                continue
+
+            yield file_name
+
+    has_forbidden_git_untracked_files = any(
+        # Don't report the environment this session is running in
+        not untracked_file.startswith('.nox/build-release/')
+        for untracked_file in get_git_untracked_files()
     )
-    if has_git_untracked_files:
+    if has_forbidden_git_untracked_files:
         session.error(
             "There are untracked files in the working directory. "
             "Remove them and try again",