Update bundled plugin-update-checker to v5.7 and remove broken setBranch() call

The bundled PUC was missing the setBranch() method on the main UpdateChecker
class (it's only on Vcs\PluginUpdateChecker via the VcsCheckerMethods trait).
When called with a non-VCS URL like the Gitea update URL, this caused a fatal
error at plugin activation.

Updating to PUC v5.7 (May 2026) which is the latest upstream release. The
setBranch() call is removed because PUC doesn't recognize Gitea as a VCS host;
the plugin falls back to PUC's plain JSON metadata mode, which is fine for a
plugin hosted on a self-managed repo.

includes/plugin-update-checker/languages/plugin-update-checker-zh_CN.po

@@ -1,57 +1,57 @@
 msgid ""
 msgstr ""
 "Project-Id-Version: plugin-update-checker\n"
-"POT-Creation-Date: 2022-01-29 12:09+0800\n"
-"PO-Revision-Date: 2022-01-29 12:10+0800\n"
+"POT-Creation-Date: 2025-11-21 10:40+0800\n"
+"PO-Revision-Date: 2025-11-21 10:40+0800\n"
 "Last-Translator: Seaton Jiang <hi@seatonjiang.com>\n"
 "Language-Team: \n"
 "Language: zh_CN\n"
 "MIME-Version: 1.0\n"
 "Content-Type: text/plain; charset=UTF-8\n"
 "Content-Transfer-Encoding: 8bit\n"
-"X-Generator: Poedit 2.4.3\n"
-"X-Poedit-Basepath: ..\n"
 "Plural-Forms: nplurals=1; plural=0;\n"
+"X-Generator: Poedit 3.8\n"
+"X-Poedit-Basepath: ..\n"
 "X-Poedit-SourceCharset: UTF-8\n"
 "X-Poedit-KeywordsList: __;_e;_x:1,2c;_x\n"
 "X-Poedit-SearchPath-0: .\n"
 
-#: Puc/v4p11/Plugin/Ui.php:54
+#: Puc/v5p6/Plugin/Ui.php:56
 msgid "View details"
 msgstr "查看详情"
 
-#: Puc/v4p11/Plugin/Ui.php:77
+#: Puc/v5p6/Plugin/Ui.php:79
 #, php-format
 msgid "More information about %s"
 msgstr "%s 的更多信息"
 
-#: Puc/v4p11/Plugin/Ui.php:128
+#: Puc/v5p6/Plugin/Ui.php:130
 msgid "Check for updates"
 msgstr "检查更新"
 
-#: Puc/v4p11/Plugin/Ui.php:214
+#: Puc/v5p6/Plugin/Ui.php:217
 #, php-format
 msgctxt "the plugin title"
 msgid "The %s plugin is up to date."
 msgstr "%s 目前是最新版本。"
 
-#: Puc/v4p11/Plugin/Ui.php:216
+#: Puc/v5p6/Plugin/Ui.php:219
 #, php-format
 msgctxt "the plugin title"
 msgid "A new version of the %s plugin is available."
 msgstr "%s 当前有可用的更新。"
 
-#: Puc/v4p11/Plugin/Ui.php:218
+#: Puc/v5p6/Plugin/Ui.php:221
 #, php-format
 msgctxt "the plugin title"
 msgid "Could not determine if updates are available for %s."
 msgstr "%s 无法确定是否有可用的更新。"
 
-#: Puc/v4p11/Plugin/Ui.php:224
+#: Puc/v5p6/Plugin/Ui.php:227
 #, php-format
 msgid "Unknown update checker status \"%s\""
 msgstr "未知的更新检查状态：%s"
 
-#: Puc/v4p11/Vcs/PluginUpdateChecker.php:100
+#: Puc/v5p6/Vcs/PluginUpdateChecker.php:113
 msgid "There is no changelog available."
 msgstr "没有可用的更新日志。"