Update from PG9.3/Postgis 2.2 to PG11/Postgis 2.5.2 fails due to ST_Union update

[Algunenano]

Mail: ​https://lists.osgeo.org/pipermail/postgis-users/2019-November/043751.html

If I try to upgrade I obtain this error : 
$ psql -d OSU -c "ALTER EXTENSION postgis UPDATE;"
ERROR:  function "st_union(geometry)" does not exist
LINE 2:  WHERE oid = 'st_union(geometry)'::regprocedure AND proparal...
                     ^
QUERY:  UPDATE pg_proc SET proparallel = 's'
	WHERE oid = 'st_union(geometry)'::regprocedure AND proparallel = 'u'
CONTEXT:  PL/pgSQL function inline_code_block line 5 at SQL statement

Affected 2.4+

In 2.4 and 2.5: postgis/postgis_drop_after.sql In 3.0 and master: postgis/postgis_after_upgrade.sql

A try catch should be enough to be able to continue if st_union(geometry) doesn't exist.

[Algunenano]

GH PR: ​https://github.com/postgis/postgis/pull/517

[Raúl Marín <git@…>]

In 5887c91/git:

Avoid throwing during update if st_union(geometry) doesn't exist

Closes ​https://github.com/postgis/postgis/pull/517
References #4588

[Raúl Marín <git@…>]

In 1e39cf0/git:

Avoid throwing during update if st_union(geometry) doesn't exist

References #4588

[Raúl Marín <git@…>]

In a4a040c/git:

Avoid throwing during update if st_union(geometry) doesn't exist

References #4588

[Raúl Marín <git@…>]

In b1732eb/git:

Avoid throwing during update if st_union(geometry) doesn't exist

References #4588

[Algunenano]

Pushed to all affected branches