fix(exts): handle pg_upgrade generated update_extensions.sql script in the extension tests

pg_upgrade may generate an update_extensions.sql script to update extensions after a major version upgrade. 
This commit modifies the extension tests to check for the presence of this script after upgrading PostgreSQL to version 17. 
If the script exists, it is executed to ensure that the extensions are updated correctly.

Author: jfroche

nix/ext/tests/default.nix

@@ -188,13 +188,25 @@ let
           with subtest("Check pg_regress with postgresql 15 after installing the last version"):
             test.check_pg_regress(Path("${psql_15}/lib/pgxs/src/test/regress/pg_regress"), "15", pg_regress_test_name)
 
+          has_update_script = False
           with subtest("switch to postgresql 17"):
             server.succeed(
               f"{pg17_configuration}/bin/switch-to-configuration test >&2"
             )
+            has_update_script = server.succeed(
+              "test -f /var/lib/postgresql/update_extensions.sql && echo 'yes' || echo 'no'"
+            ).strip() == "yes"
+            if has_update_script:
+              # Run the extension update script generated during the upgrade
+              test.run_sql_file("/var/lib/postgresql/update_extensions.sql")
 
           with subtest("Check last version of the extension after postgresql upgrade"):
-            test.assert_version_matches(last_version)
+            if has_update_script:
+              # If there was an update script, the last version should be installed
+              test.assert_version_matches(versions["17"][-1])
+            else:
+              # Otherwise, the version should match the last version from postgresql 15
+              test.assert_version_matches(last_version)
 
           with subtest("Check upgrade path with postgresql 17"):
             test.check_upgrade_path("17")