fix spack external find for Python >= 3.13 (#48170)

Python >= 3.13 does not have the crypt variant anymore. Still no matter
if the test for crypt succeeds (which it can on Fedora providing its own
crypt module for Python 3.13) or fails, it will add +crypt or ~crypt,
which both fail because the variant only exists until Python 3.12.

Co-authored-by: Richard Berger <rberger@lanl.gov>

var/spack/repos/builtin/packages/python/package.py

@@ -364,7 +364,7 @@ def determine_variants(cls, exes, version_str):
                 variants += "~tix"
 
         # Some modules are platform-dependent
-        if sys.platform != "win32":
+        if sys.platform != "win32" and Version(version_str) < Version("3.13"):
             try:
                 python("-c", "import crypt", error=os.devnull)
                 variants += "+crypt"