More fixups for pg_upgrade cross-version tests.

Commit 7ca37fb removed regress_putenv from the regress.so library,
so reloading a SQL function dependent on that would not work.
Fix similarly to 52202bb.

Per buildfarm.

Author: tglsfdc

src/bin/pg_upgrade/test.sh

@@ -178,6 +178,8 @@ if "$MAKE" -C "$oldsrc" installcheck-parallel; then
 		fix_sql="$fix_sql
 				 DROP FUNCTION IF EXISTS
 					public.oldstyle_length(integer, text);	-- last in 9.6
+				 DROP FUNCTION IF EXISTS
+					public.putenv(text);	-- last in v13
 				 DROP OPERATOR IF EXISTS	-- last in v13
 					public.#@# (pg_catalog.int8, NONE),
 					public.#%# (pg_catalog.int8, NONE),