Update copyright for 2021

Backpatch-through: 9.5

src/backend/optimizer/prep/prepagg.c

@@ -22,7 +22,7 @@
  * at executor startup.  The Agg nodes are constructed much later in the
  * planning, however, so it's not trivial.
  *
- * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  *

src/backend/optimizer/prep/prepjointree.c

@@ -14,7 +14,7 @@
  *		remove_useless_result_rtes
  *
  *
- * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  *

src/backend/optimizer/prep/prepqual.c

@@ -19,7 +19,7 @@
  * tree after local transformations that might introduce nested AND/ORs.
  *
  *
- * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  *

src/backend/optimizer/prep/preptlist.c

@@ -29,7 +29,7 @@
  * that because it's faster in typical non-inherited cases.
  *
  *
- * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION

src/backend/optimizer/prep/prepunion.c

@@ -12,7 +12,7 @@
  * case, but most of the heavy lifting for that is done elsewhere,
  * notably in prepjointree.c and allpaths.c.
  *
- * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  *