title: ST_ApproximateMedialAxis(geometry) does not exist?
body: <p>Not make sense, the <a href="https://postgis.net/docs/ST_ApproximateMedialAxis.html" rel="nofollow noreferrer">function exists since v2.2</a>,</p>
  <pre class="lang-sql prettyprint-override"><code>SELECT distinct geometrytype(geom) from t; --  POLYGON
  SELECT ST_ApproximateMedialAxis(geom) from t;
  -- ERROR:  function st_approximatemedialaxis(geometry) does not exist
  -- LINE 1: select ST_ApproximateMedialAxis(geom) from t...
  </code></pre>
  <hr />
  <ul>
  <li><p><code>select PostGIS_Version()</code> =  &quot;3.0 USE_GEOS=1 USE_PROJ=1 USE_STATS=1&quot;</p>
  </li>
  <li><p><code>select select postgis_full_version()</code> = <em>POSTGIS=&quot;3.0.1 ec2a9aa&quot; [EXTENSION] PGSQL=&quot;120&quot; GEOS=&quot;3.8.0-CAPI-1.13.1 &quot; PROJ=&quot;6.3.1&quot; LIBXML=&quot;2.9.10&quot; LIBJSON=&quot;0.13.1&quot; LIBPROTOBUF=&quot;1.3.3&quot; WAGYU=&quot;0.4.3 (Internal)</em></p>
  </li>
  <li><p><code>select Version()</code> = &quot;PostgreSQL 12.3 (Ubuntu 12.3-1.pgdg20.04+1) ... 64-bit&quot;</p>
  </li>
  <li><p><code>\df st_area</code>, and all other are there...</p>
  </li>
  <li><p><code>\df public.ST_ApproximateMedialAxis</code> = no function!</p>
  </li>
  </ul>
  <p>This last check shows that was not installed (!)... Well, the guide say <em>&quot;This method needs SFCGAL backend&quot;</em>, how to check it?</p>