requirements: Pin tree_sitter to < 0.22.0

Latest tree_sitter release removed the Language.build_library method that swh-search uses to compile the search language parsing library.

So restrict tree_sitter version until a solution is found to support latest release.

requirements.txt

@@ -2,7 +2,7 @@
 # should match https://pypi.python.org/pypi names. For the full spec or
 # dependency lines, see https://pip.readthedocs.org/en/1.1/requirements.html
 click
-elasticsearch>=7.0.0,<8.0.0
+elasticsearch >= 7.0.0, < 8.0.0
 typing-extensions
-tree_sitter
+tree_sitter < 0.22.0
 iso8601