Fix URI escaping, which should actually be "%s", not "%p"

See <https://discourse.phabricator-community.org/t/projects-workboards-links-issue/2896>.

The documentation on `urisprintf()` isn't very clear here, I'll update it in
a followup. "%p" is for cases like encoding a branch name (which may contain
slashes) as a single path component in a URI.

src/applications/project/state/PhabricatorWorkboardViewState.php

@@ -103,7 +103,7 @@ final class PhabricatorWorkboardViewState
 
   public function newWorkboardURI($path = null) {
     $project = $this->getProject();
-    $uri = urisprintf('%p%p', $project->getWorkboardURI(), $path);
+    $uri = urisprintf('%s%s', $project->getWorkboardURI(), $path);
     return $this->newURI($uri);
   }