srfi-64.html: Add missing space between arguments.

This space was removed from the procedure name in commit
05376fd ("srfi-64.html: Fix typos."), but a space is needed for the
HTML presentation; re-add it in-between the the procedure name and its
first argument.

Author: apteryks

srfi-64.html

@@ -536,7 +536,7 @@ <h4>Running specific tests with a specified runner</h4>
 <code>test-apply</code> <em>and</em> does not match any
 active <code>test-skip</code> specifiers.</p>
 <p>
-<code>(<b>test-with-runner</b><var>runner</var> <var>decl-or-expr</var> ...)</code><br />
+<code>(<b>test-with-runner</b> <var>runner</var> <var>decl-or-expr</var> ...)</code><br />
 Executes each <var>decl-or-expr</var> in order in a context
 where the current test-runner is <var>runner</var>.</p>