PgsqlRequirements::getRequirements() reports a PostgreSQL extension as "Not created" when it is not available

Problem/Motivation

PgsqlRequirements::getRequirements() uses the following code.

// If the extension is not available, set the requirement error.
if (!$connection->schema()->extensionExists('pg_trgm')) {
  $requirements['pgsql_extension_pg_trgm']['severity'] = RequirementSeverity::Error;
  $requirements['pgsql_extension_pg_trgm']['value'] = t('Not created');
  $requirements['pgsql_extension_pg_trgm']['description'] = t('The <a href=":pg_trgm">pg_trgm</a> PostgreSQL extension is not present. The extension is required by Drupal to improve performance when using PostgreSQL. See <a href=":requirements">Drupal database server requirements</a> for more information.', [
    ':pg_trgm' => 'https://www.postgresql.org/docs/current/pgtrgm.html',
    ':requirements' => 'https://www.drupal.org/docs/system-requirements/database-server-requirements',
  ]);
}

When the extension is not available, it shows Not created.

Proposed resolution

Change that code to the following one.

// If the extension is not available, set the requirement error.
if (!$connection->schema()->extensionExists('pg_trgm')) {
  $requirements['pgsql_extension_pg_trgm']['severity'] = RequirementSeverity::Error;
  $requirements['pgsql_extension_pg_trgm']['value'] = t('Not available');
  $requirements['pgsql_extension_pg_trgm']['description'] = t('The <a href=":pg_trgm">pg_trgm</a> PostgreSQL extension is not present. The extension is required by Drupal to improve performance when using PostgreSQL. See <a href=":requirements">Drupal database server requirements</a> for more information.', [
    ':pg_trgm' => 'https://www.postgresql.org/docs/current/pgtrgm.html',
    ':requirements' => 'https://www.drupal.org/docs/system-requirements/database-server-requirements',
  ]);
}

Instead of t('Not created'), it uses t('Not available'), which is more correct, since a database engine extension is not created.