Error out if incompatible DBAL version is detected

doctrine/dbal is an optional dependency of laravel/framework, and v3 of
the DBAL has been released recently, but obviously, Laravel 6 was never
meant to be compatible with that version.
Users still using Laravel 6 and updating their dependencies get confused
and file invalid reports on the DBAL, see for instance
doctrine/dbal#4439
or
doctrine/dbal#4757

Fixes #24271

src/Illuminate/Database/SQLiteConnection.php

@@ -7,6 +7,7 @@
 use Illuminate\Database\Query\Processors\SQLiteProcessor;
 use Illuminate\Database\Schema\Grammars\SQLiteGrammar as SchemaGrammar;
 use Illuminate\Database\Schema\SQLiteBuilder;
+use LogicException;
 
 class SQLiteConnection extends Connection
 {
@@ -85,6 +86,12 @@ protected function getDefaultPostProcessor()
      */
     protected function getDoctrineDriver()
     {
+        if (! class_exists(DoctrineDriver::class)) {
+            throw new LogicException(
+                'Laravel v6 is only compatible with doctrine/dbal 2, lock it to that version with composer require doctrine/dbal "^2.0"'
+            );
+        }
+
         return new DoctrineDriver;
     }