Require PHP 7.4+ (#5720)

* Require PHP 7.4+
https://github.com/FreshRSS/FreshRSS/discussions/5474

* Update Docker oldest
Alpine 3.13 with PHP 7.4.26

* Add missing packets to Docker oldest

* Update to typed properties
https://php.net/migration74.new-features#migration74.new-features.core.typed-properties

* More types

app/Models/ViewJavascript.php

@@ -5,14 +5,12 @@ declare(strict_types=1);
 final class FreshRSS_ViewJavascript extends FreshRSS_View {
 
 	/** @var array<FreshRSS_Category> */
-	public $categories;
+	public array $categories;
 	/** @var array<FreshRSS_Feed> */
-	public $feeds;
+	public array $feeds;
 	/** @var array<FreshRSS_Tag> */
-	public $tags;
+	public array $tags;
 
-	/** @var string */
-	public $nonce;
-	/** @var string */
-	public $salt1;
+	public string $nonce;
+	public string $salt1;
 }