BUG: Loosen importlib metadata dependency version range

This package is a backport of part of the core library in 3.10, so
is extremely stable.  It will no longer be required in a year,
when 3.9 reaches EOL.  In the meantime, it is causing plenty of
failures of pysindy installs.  See dynamicslab/pysindy#547 and
coments on dynamicslab/pysindy#529.

pyproject.toml

@@ -19,7 +19,7 @@ python = "^3.9"
 numpy = "^1.18.3"
 scipy = "^1.4.1"
 scikit-learn = "^1"
-importlib-metadata = "^7.1.0"
+importlib-metadata = ">=7.1.0"
 
 # docs
 sphinx = {version = "^5", optional = true}