Fix typos in comments, code and documentation

While on it, newlines are removed from the end of two elog() strings.
The others are simple grammar mistakes.  One comment in pg_upgrade
referred incorrectly to sequences since a7e5457.

Author: Justin Pryzby
Discussion: https://postgr.es/m/20221230231257.GI1153@telsasoft.com
Backpatch-through: 11

doc/src/sgml/parallel.sgml

@@ -128,7 +128,7 @@ EXPLAIN SELECT * FROM pgbench_accounts WHERE filler LIKE '%x%';
 
   <para>
     In addition, the system must not be running in single-user mode.  Since
-    the entire database system is running in single process in this situation,
+    the entire database system is running as a single process in this situation,
     no background workers will be available.
   </para>
 

doc/src/sgml/ref/alter_table.sgml

@@ -944,7 +944,7 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
       constraint. This does not work, however, if any of the partition keys
       is an expression and the partition does not accept
       <literal>NULL</literal> values. If attaching a list partition that will
-      not accept <literal>NULL</literal> values, also add
+      not accept <literal>NULL</literal> values, also add a
       <literal>NOT NULL</literal> constraint to the partition key column,
       unless it's an expression.
      </para>

doc/src/sgml/sources.sgml

@@ -921,8 +921,8 @@ BETTER: unrecognized node type: 42
    <simplesect>
     <title>Function-Like Macros and Inline Functions</title>
     <para>
-     Both, macros with arguments and <literal>static inline</literal>
-     functions, may be used. The latter are preferable if there are
+     Both macros with arguments and <literal>static inline</literal>
+     functions may be used. The latter are preferable if there are
      multiple-evaluation hazards when written as a macro, as e.g., the
      case with
 <programlisting>