Merge branch '4.4'

* 4.4: (23 commits)
  [HttpFoundation] fix docblock
  [HttpKernel] Flatten "exception" controller argument if not typed
  Fix MySQL column type definition.
  Link the right file depending on the new version
  [Cache] Redis Tag Aware warn on wrong eviction policy
  [HttpClient] fix HttpClientDataCollector
  [HttpKernel] collect bundle classes, not paths
  [Config] fix id-generation for GlobResource
  [HttpKernel] dont check cache freshness more than once per process
  [Finder] Allow ssh2 stream wrapper for sftp
  [FrameworkBundle] fix wiring of httplug client
  add FrameworkBundle requirement
  [SecurityBundle] add tests with empty authenticator
  [Security] always check the token on non-lazy firewalls
  [DI] Use reproducible entropy to generate env placeholders
  [WebProfilerBundle] Require symfony/twig-bundle
  [Mailer] Add UPGRADE entry about the null transport DSN
  bumped Symfony version to 4.3.9
  updated VERSION for 4.3.8
  updated CHANGELOG for 4.3.8
  ...

Author: nicolas-grekas

CHANGELOG.md

@@ -4,6 +4,7 @@ CHANGELOG
 4.4.0
 -----
 
+ * [BC BREAK] changed the `NullTransport` DSN from `smtp://null` to `null://null`
  * [BC BREAK] renamed `SmtpEnvelope` to `Envelope`, renamed `DelayedSmtpEnvelope` to
    `DelayedEnvelope`
  * [BC BREAK] changed the syntax for failover and roundrobin DSNs