fix: compare sponsor_info as bool instead of string (#446)

Relates to github-community-projects/cleanowners#373

## What

Changed the sponsor_info gate in contributors.py from a string comparison
(`== "true"`) to a truthy check, and updated the test mock to return a
bool to match what get_bool_env_var actually returns.

## Why

get_bool_env_var returns a Python bool, but the comparison checked for
the string "true". Since `True == "true"` is always False, sponsor
information was never fetched regardless of the SPONSOR_INFO env var
setting.

## Notes

- markdown.py already has `_is_truthy()` that handles both types, so the
  rendering side was not affected — only the data fetch was skipped.
- json_writer.py passes sponsor_info through without comparison, so it's
  also unaffected.

Signed-off-by: jmeridth <jmeridth@gmail.com>

Author: jmeridth

contributors.py

@@ -69,7 +69,7 @@ def main():
             )
 
     # Get sponsor information on the contributor
-    if sponsor_info == "true":
+    if sponsor_info:
         contributors = contributor_stats.get_sponsor_information(
             contributors, token, ghe
         )

test_contributors.py

@@ -419,7 +419,7 @@ def test_main_fetches_sponsor_info_when_enabled(self):
                 "",
                 "",
                 "",
-                "true",
+                True,
                 False,
                 "contributors.md",
                 False,