test-config-case: print only the Section we're interested in.

This allows us to add additional settings to the global hgrc file
created by run-tests.py without breaking this test.

tests/test-config-case

@@ -1,7 +1,7 b''
 #!/bin/sh
 
 echo '[Section]' >> $HGRCPATH
 echo 'KeY = Case Sensitive' >> $HGRCPATH
 echo 'key = lower case' >> $HGRCPATH
 
-hg showconfig
+hg showconfig Section