Fix XML id to match GUC name

For some reason, the id of the description of
max_parallel_maintenance_workers has been
guc-max-parallel-workers-maintenance since the beginning.  Flip that
around to make it consistent.

doc/src/sgml/config.sgml

@@ -2367,7 +2367,7 @@ include_dir 'conf.d'
         <para>
          When changing this value, consider also adjusting
          <xref linkend="guc-max-parallel-workers"/>,
-         <xref linkend="guc-max-parallel-workers-maintenance"/>, and
+         <xref linkend="guc-max-parallel-maintenance-workers"/>, and
          <xref linkend="guc-max-parallel-workers-per-gather"/>.
         </para>
        </listitem>
@@ -2415,7 +2415,7 @@ include_dir 'conf.d'
        </listitem>
       </varlistentry>
 
-      <varlistentry id="guc-max-parallel-workers-maintenance" xreflabel="max_parallel_maintenance_workers">
+      <varlistentry id="guc-max-parallel-maintenance-workers" xreflabel="max_parallel_maintenance_workers">
        <term><varname>max_parallel_maintenance_workers</varname> (<type>integer</type>)
        <indexterm>
         <primary><varname>max_parallel_maintenance_workers</varname> configuration parameter</primary>
@@ -2464,7 +2464,7 @@ include_dir 'conf.d'
          Sets the maximum number of workers that the system can support for
          parallel operations.  The default value is 8.  When increasing or
          decreasing this value, consider also adjusting
-         <xref linkend="guc-max-parallel-workers-maintenance"/> and
+         <xref linkend="guc-max-parallel-maintenance-workers"/> and
          <xref linkend="guc-max-parallel-workers-per-gather"/>.
          Also, note that a setting for this value which is higher than
          <xref linkend="guc-max-worker-processes"/> will have no effect,

doc/src/sgml/ref/create_index.sgml

@@ -771,7 +771,7 @@ Indexes:
    least a <literal>32MB</literal> share of the total
    <varname>maintenance_work_mem</varname> budget.  There must also be
    a remaining <literal>32MB</literal> share for the leader process.
-   Increasing <xref linkend="guc-max-parallel-workers-maintenance"/>
+   Increasing <xref linkend="guc-max-parallel-maintenance-workers"/>
    may allow more workers to be used, which will reduce the time
    needed for index creation, so long as the index build is not
    already I/O bound.  Of course, there should also be sufficient

doc/src/sgml/ref/vacuum.sgml

@@ -239,7 +239,7 @@ VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] [ ANALYZE ] [ <replaceable class="paramet
       (without <literal>FULL</literal>), if the <literal>PARALLEL</literal> option
       is omitted, then the number of workers is determined based on the number of
       indexes on the relation that support parallel vacuum operation and is further
-      limited by <xref linkend="guc-max-parallel-workers-maintenance"/>.  An index
+      limited by <xref linkend="guc-max-parallel-maintenance-workers"/>.  An index
       can participate in parallel vacuum if and only if the size of the index is
       more than <xref linkend="guc-min-parallel-index-scan-size"/>.  Please note
       that it is not guaranteed that the number of parallel workers specified in