lang/spidermonkey91: limit Python version to 3.7-3.10 (+)

Old firefox engine still have harcoded 'rU' as file mode for 'fopen()'
'U' is default and deprecated since python-3.3, becomes a failure in 3.11.

Instead of patching dozen files, limit python to 3.7-3.10 as it used only for configure stage.

Approved by: portmgr blanket