bug #40376 [Messenger] Don't lock tables or start transactions (Nyholm)

This PR was merged into the 5.2 branch.

Discussion
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[Messenger] Don't lock tables or start transactions

| Q             | A
| ------------- | ---
| Branch?       | 5.2
| Bug fix?      | yes
| New feature?  | no
| Deprecations? | no
| Tickets       |
| License       | MIT
| Doc PR        |

I was so sure my PR #40336 fixed the doctrine-messenger issue once and for all. But it had a very silent bug..

This has been tricky to debug and find because the `PDO` behaves differently in PHP 7.4 compared to PHP 8.

| Scenario | Command | Is executed in transaction | Method that calls `PostgreSqlConnection::getTriggerSql()` |
| --| -- | -- | -- |
| A | `messenger:setup-transports` | No | `setup()`
| B| `doctrine:schema:create` | No | `getExtraSetupSqlForTable()`
| C | `doctrine:migration:diff` | Yes by default, but it can be configured | `getExtraSetupSqlForTable()`

PR #40055 fixed scenario C on PHP 8, but that also broke scenario B on PHP 7.4 and PHP 8.
In PR #40336 I was wrong claiming:

> We don't need COMMIT because the transaction will commit itself when we close the connection.

The result was the we removed all the errors messages from the 3 scenarios. But scenario B will produce some SQL that is actually never committed. IE it will silently fail.

I've been trying to figure out a good solution to how or when to start a transaction. I tried out @fbourigault [suggestion](https://github.com/symfony/symfony/pull/40336#issuecomment-790622951) but that would be the same fix as #40055.

---------------

We need a transaction because the SQL includes a `LOCK TABLE`, however, I cannot see a strict need for it. This PR removes `LOCK TABLE` and all transaction juggling. It all seams to work.

I would be happy to get thorough feedback on this PR so we can end the chapter of constantly adding bugs to this part of the component.

@dunglas, you added `LOCK TABLE` in your initial version of this class in https://github.com/symfony/symfony/pull/35485, could you share some knowledge if this is a good or bad idea?

Commits
-------

26061a131d Dont lock tables or start transactions

src/Symfony/Component/Messenger/Bridge/Doctrine/Tests/Transport/PostgreSqlConnectionTest.php

@@ -51,16 +51,10 @@ class PostgreSqlConnectionTest extends TestCase
         $table->addOption('_symfony_messenger_table_name', 'queue_table');
         $sql = implode("\n", $connection->getExtraSetupSqlForTable($table));
 
-        /*
-         * We need to start a transaction for the following commands to work properly:
-         * doctrine:schema:create
-         * messenger:setup-transports
-         * doctrine:migrations:diff and doctrine:migrations:migrate
-         */
-        $this->assertStringContainsString('BEGIN;', $sql);
         $this->assertStringContainsString('CREATE TRIGGER', $sql);
 
-        // We MUST NOT commit, that will mess with the PDO in PHP 8
+        // We MUST NOT use transaction, that will mess with the PDO in PHP 8
+        $this->assertStringNotContainsString('BEGIN;', $sql);
         $this->assertStringNotContainsString('COMMIT;', $sql);
     }
 

src/Symfony/Component/Messenger/Bridge/Doctrine/Transport/PostgreSqlConnection.php

@@ -109,8 +109,6 @@ final class PostgreSqlConnection extends Connection
     private function getTriggerSql(): array
     {
         return [
-            'BEGIN;',
-            sprintf('LOCK TABLE %s;', $this->configuration['table_name']),
             // create trigger function
             sprintf(<<<'SQL'
 CREATE OR REPLACE FUNCTION notify_%1$s() RETURNS TRIGGER AS $$