Tests: Error on no test files being found for render_report.py

This commit checks the total number of files being processed for
rendering tests and causes it to emit a failure if none are found. This
has the benefit of loudly failing if there is a configuration error
instead of succeeding.

Pull Request: https://projects.blender.org/blender/blender/pulls/133691

tests/python/modules/render_report.py

@@ -550,6 +550,10 @@ class Report:
         silently_failed_tests = []
         all_files = list(blend_list(dirpath, self.device, self.blocklist))
         all_files.sort()
+        if not list(blend_list(dirpath, self.device, [])):
+            print_message("No .blend files found in '{}'!".format(dirpath), 'FAILURE', 'FAILED')
+            return False
+
         print_message("Running {} tests from 1 test case." .
                       format(len(all_files)),
                       'SUCCESS', "==========")