Fix blob binding overwrite on DB2

On DB2 when binding more than 1 blob in the same statement each subsequent blob overwrites previous one.
So instead of [1, 2, 3] we get [2, 3, 3]
This happens because of reference between loop variable `$value` and the item in `$this->parameters[]`,
which remains after iteration, see `bindLobs` and `bind` methods in `\Doctrine\DBAL\Driver\IBMDB2\Statement`

src/Driver/IBMDB2/Statement.php

@@ -182,6 +182,8 @@ private function bindLobs(): array
             } else {
                 $this->bind($param, $value, DB2_PARAM_IN, DB2_CHAR);
             }
+
+            unset($value);
         }
 
         return $handles;

tests/Functional/BlobTest.php

@@ -169,6 +169,34 @@ public function testBindParamProcessesStream(): void
         $this->assertBlobContains('test');
     }
 
+    public function testBlobBindingDoesNotOverwritePrevious(): void
+    {
+        $table = new Table('blob_table');
+        $table->addColumn('id', 'integer');
+        $table->addColumn('blobcolumn1', 'blob', ['notnull' => false]);
+        $table->addColumn('blobcolumn2', 'blob', ['notnull' => false]);
+        $table->setPrimaryKey(['id']);
+        $this->dropAndCreateTable($table);
+
+        $params = ['test1', 'test2'];
+        $this->connection->executeStatement(
+            'INSERT INTO blob_table(id, blobcolumn1, blobcolumn2) VALUES (1, ?, ?)',
+            $params,
+            [ParameterType::LARGE_OBJECT, ParameterType::LARGE_OBJECT],
+        );
+
+        $blobs = $this->connection->fetchNumeric('SELECT blobcolumn1, blobcolumn2 FROM blob_table');
+        self::assertIsArray($blobs);
+
+        $actual = [];
+        foreach ($blobs as $blob) {
+            $blob     = Type::getType('blob')->convertToPHPValue($blob, $this->connection->getDatabasePlatform());
+            $actual[] = stream_get_contents($blob);
+        }
+
+        self::assertEquals(['test1', 'test2'], $actual);
+    }
+
     private function assertBlobContains(string $text): void
     {
         [, $blobValue] = $this->fetchRow();