sysupdate: tighten component_name_valid() mildly

Let's make sure that we can still generate a component enablement
drop-in for any component that might be defined.

src/sysupdate/sysupdate-util.c

@@ -52,7 +52,7 @@ bool component_name_valid(const char *c) {
                 return false;
 
         /* Stack allocation is safe, since STRING_FILENAME_PART includes a length check */
-        const char *j = strjoina("sysupdate.", c, ".d");
+        const char *j = strjoina("sysupdate.", c, ".component.d");
 
         return filename_is_valid(j);
 }