Merge pull request #25206 from compnerd/interpretive-dance

test: execute `rth` with the interpreter

Author: compnerd

test/lit.cfg

@@ -1488,7 +1488,7 @@ config.substitutions.append(('%gyb', '%r %s' % (sys.executable, config.gyb)))
 config.substitutions.append(('%round-trip-syntax-test',
                              '%r %s' % (sys.executable,
                                         config.round_trip_syntax_test)))
-config.substitutions.append(('%rth', config.rth))
+config.substitutions.append(('%rth', '%r %s' % (sys.executable, config.rth)))
 config.substitutions.append(('%scale-test',
                              '{} --swiftc-binary={} --tmpdir=%t'.format(
                                  config.scale_test, config.swiftc)))