stack/slapos: restore an old pin of importlib-metadata for py2

1c4a3c69 (stack/slapos.cfg: version up eggs (requests 2.31.0 and
friends), 2023-10-04) broke component/nxdtest/test-py2.cfg and
others using pytest on python2

stack/slapos.cfg

@@ -365,6 +365,7 @@ Flask = 1.1.2
 gitdb2 = 2.0.5
 GitPython = 2.1.11
 idna = 2.9
+importlib-metadata = 1.7.0:whl
 itsdangerous = 0.24
 Jinja2 = 2.11.3
 jsonschema = 3.0.2:whl