pgAdmin 4 commit: Fixed an issue where fetching the schema throws an er

Fixed an issue where fetching the schema throws an error if the database
is not connected in Schema Diff. Fixes #5673

Maintenance Database is selected by default in Schema Diff.

Branch
------
master

Details
-------
https://git.postgresql.org/gitweb?p=pgadmin4.git;a=commitdiff;h=2469032f15f6317aba21a3e63836d1f8933e7c23

Modified Files
--------------
docs/en_US/release_notes_4_24.rst                    |  3 ++-
web/pgadmin/tools/schema_diff/__init__.py            | 20 +++++++++++---------
.../tools/schema_diff/static/js/schema_diff_ui.js    | 12 ++++++++----
3 files changed, 21 insertions(+), 14 deletions(-)