Python 3.10 fixes, part 2

There was a fallback case I overlooked in the initial patch, with
a similarly imperfect version extractor.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Rich Ercolani <rincebrain@gmail.com>
Closes #12045 
Closes #12673

config/ax_python_devel.m4

@@ -224,7 +224,7 @@ EOD`
 				ac_python_version=$PYTHON_VERSION
 			else
 				ac_python_version=`$PYTHON -c "import sys; \
-					print (sys.version[[:3]])"`
+					print ('.'.join(sys.version.split('.')[[:2]]))"`
 			fi
 		fi