test: move test_ruby() inside the only client

Not much point in polluting the main library, and also will be useful to
modify it in tandem with the tests.

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>

test/T395-ruby.sh

@@ -8,6 +8,10 @@ fi
 
 add_email_corpus
 
+test_ruby() {
+    MAIL_DIR=$MAIL_DIR $NOTMUCH_RUBY -I "$NOTMUCH_BUILDDIR/bindings/ruby"> OUTPUT
+}
+
 test_begin_subtest "compare thread ids"
 test_ruby <<"EOF"
 require 'notmuch'

test/test-lib.sh

@@ -1124,10 +1124,6 @@ test_python() {
 	$NOTMUCH_PYTHON -B - > OUTPUT
 }
 
-test_ruby() {
-    MAIL_DIR=$MAIL_DIR $NOTMUCH_RUBY -I "$NOTMUCH_BUILDDIR/bindings/ruby"> OUTPUT
-}
-
 test_C () {
     local exec_file test_file
     exec_file="test${test_count}"