Make javadoc <p> style guide compliant

This led to confusion for an open source contributor about how to format
code. We don't want to be like, "do as I say, not as I do."

https://google.github.io/styleguide/javaguide.html#s7.1.2-javadoc-paragraphs
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=122589700

java/google/registry/model/server/ServerSecret.java

@@ -42,8 +42,8 @@ public class ServerSecret extends CrossTldSingleton {
 
   /**
    * Get the server secret, creating it if the datastore doesn't have one already.
-   * <p>
-   * There's a tiny risk of a race here if two calls to this happen simultaneously and create
+   *
+   * <p>There's a tiny risk of a race here if two calls to this happen simultaneously and create
    * different keys, in which case one of the calls will end up with an incorrect key. However, this
    * happens precisely once in the history of the system (after that it's always in datastore) so
    * it's not worth worrying about.