[gardening] Fix recently introduced typo: "propogated" → "propagated"

tools/SourceKit/tools/sourcekitd-test/sourcekitd-test.cpp

@@ -402,7 +402,7 @@ static int handleTestInvocation(ArrayRef<const char *> Args,
   switch (Opts.Request) {
   case SourceKitRequest::None:
     llvm::errs() << "request is not set\n";
-    // FIXME: This non-zero return value is not propogated as an exit code.
+    // FIXME: This non-zero return value is not propagated as an exit code.
     //        In other words, despite returning 1 here, the program still exits
     //        with a zero (successful) exit code.
     return 1;