DOC: Demote logging about non-matching glob to warning

The expand_globs function from conda_build.utils logs an ERROR
when a glob expression returns no matches, this is overly alarming
because the user may now use negative glob expressions which they
don't care if it returns empty or the user may want to use the
same set of glob expressions for multiple platforms some of which
may return empty on some platforms.

conda#5216
conda#5455

conda_build/utils.py

@@ -1275,7 +1275,7 @@ def expand_globs(
  glob_files = glob(path, recursive=True)
  if not glob_files:
  log = get_logger(__name__)
- log.error(f"Glob {path} did not match in root_dir {root_dir}")
+ log.warning(f"Glob {path} did not match in root_dir {root_dir}")
  # https://docs.python.org/3/library/glob.html#glob.glob states that
  # "whether or not the results are sorted depends on the file system".
  # Avoid this potential ambiguity by sorting. (see #4185)