Update Symfony to 7.3.7 / 6.4.29

Here's the fix for that:

diff --git a/core/tests/Drupal/Tests/Core/DrupalKernel/ValidateHostnameTest.php b/core/tests/Drupal/Tests/Core/DrupalKernel/ValidateHostnameTest.php
index 2c2ad89f4c9..7718914f10f 100644
--- a/core/tests/Drupal/Tests/Core/DrupalKernel/ValidateHostnameTest.php
+++ b/core/tests/Drupal/Tests/Core/DrupalKernel/ValidateHostnameTest.php
@@ -50,7 +50,7 @@ public static function providerTestValidateHostname() {

     // Verifies that using valid IP address for the hostname is allowed.
     $data[] = ['72.21.91.99:80', 'Properly formed HTTP_HOST with IPv4 address valid.', TRUE];
-    $data[] = ['2607:f8b0:4004:803::1002:80', 'Properly formed HTTP_HOST with IPv6 address valid.', TRUE];
+    $data[] = ['[2607:f8b0:4004:803::1002]:80', 'Properly formed HTTP_HOST with IPv6 address valid.', TRUE];

     // Verifies that the IPv6 loopback address is valid.
     $data[] = ['[::1]:80', 'HTTP_HOST containing IPv6 loopback is valid.', TRUE];

These two three issues probably need to be included in the MRs to get 11.1.x and 10.4.x to pass:

• #3539366: Default DB transaction isolation set to read-committed breaks InstallerIsolationLevelExistingSettingsTest test
• #3539331: Skip failing test with incorrect warning for system requirements about APCu memory
• #3554130: If cache exists cspell job fails

Edit: Bad references. Getting the good ones and pushing them up now.

Additionally #3484845: [random test failure] ImageUrlProviderTest::testResize for 10.4.x.

We agreed not to update 11.1.x to Symfony 7.3, so I am going to hide that MR.

    1)
    Drupal\Tests\file\Functional\DownloadTest::testPrivateFileTransferWithoutPageCache
    Correctly denied access to a file when file_test sets the header to -1.
    Failed asserting that 200 is identical to 403.

Excellent. Postponing.

Can someone tell me how this is fixing this? https://www.drupal.org/project/drupal/issues/3043779#comment-16343306

The 11.2.x, 10.5.x, and 10.4.x MRs were committed as part of today's security releases, and I've committed 10.6.x just now.

We still need an update for 11.x and 11.3.x once Symfony provides an updated beta for Symfony 7.4, but that will come naturally in a followup issue when we update the dependency as part of our normal release process.

@catch, @longwave, and I agreed not to update 11.1.x to 7.3 (as per the 11.1.9 release notes).

Thanks everyone!

This went out with https://www.drupal.org/project/drupal/releases/11.2.8

edit: apparently had this tab open a long time and crossposted.