PEP 0: Fix 'Page Source (GitHub)' (#2401)

Co-authored-by: Adam Turner <9087854+aa-turner@users.noreply.github.com>

pep_sphinx_extensions/pep_theme/templates/page.html

@@ -35,7 +35,9 @@
             <p id="toc-title">{{ title }}</p>
             {{ toc }}
             <br />
+            {%- if not sourcename.startswith("pep-0000") %}
             <a id="source" href="https://github.com/python/peps/blob/main/{{sourcename}}">Page Source (GitHub)</a>
+            {%- endif %}
         </nav>
     </section>
     <script src="{{ pathto('_static/colour_scheme.js', resource=True) }}"></script>