你好，我有一台 Linux 服务器（Debian 10 Buster）
输入命令后：sudo apt-get update进行更新
显示错误：
Hit:1 http://deb.debian.org/debian buster InRelease
Hit:2 http://deb.debian.org/debian buster-updates InRelease
Hit:3 http://security.debian.org buster/updates InRelease
Get:4 http://apt.postgresql.org/pub/repos/apt buster-pgdg InRelease [110 kB]
Ign:5 http://ppa.launchpad.net/ondrej/pkg-gearman/ubuntu impish InRelease
Get:6 http://ppa.launchpad.net/ondrej/php/ubuntu impish InRelease [23.9 kB]
Hit:7 https://packages.sury.org/php buster InRelease
Err:8 http://ppa.launchpad.net/ondrej/pkg-gearman/ubuntu impish Release
404 Not Found [IP: 1200:89c:6950:8000::17 80]
Get:9 http://apt.postgresql.org/pub/repos/apt buster-pgdg/main amd64 Packages [246 kB]
Err:6 http://ppa.launchpad.net/ondrej/php/ubuntu impish InRelease
The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 4F4E..
Reading package lists... Done
E: The repository 'http://ppa.launchpad.net/ondrej/pkg-gearman/ubuntu impish Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
W: GPG error: http://ppa.launchpad.net/ondrej/php/ubuntu impish InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 4F4E.....
E: The repository 'http://ppa.launchpad.net/ondrej/php/ubuntu impish InRelease' is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
W: Target Packages (main/binary-amd64/Packages) is configured multiple times in /etc/apt/sources.list.d/php.list:1 and /etc/apt/sources.list.d/php7.list:1
W: Target Packages (main/binary-all/Packages) is configured multiple times in /etc/apt/sources.list.d/php.list:1 and /etc/apt/sources.list.d/php7.list:1
W: Target Translations (main/i18n/Translation-en_GB) is configured multiple times in /etc/apt/sources.list.d/php.list:1 and /etc/apt/sources.list.d/php7.list:1
W: Target Translations (main/i18n/Translation-en) is configured multiple times in /etc/apt/sources.list.d/php.list:1 and /etc/apt/sources.list.d/php7.list:1
W: Target Packages (main/binary-amd64/Packages) is configured multiple times in /etc/apt/sources.list.d/php.list:1 and /etc/apt/sources.list.d/php7.list:1
W: Target Packages (main/binary-all/Packages) is configured multiple times in /etc/apt/sources.list.d/php.list:1 and /etc/apt/sources.list.d/php7.list:1
W: Target Translations (main/i18n/Translation-en_GB) is configured multiple times in /etc/apt/sources.list.d/php.list:1 and /etc/apt/sources.list.d/php7.list:1
W: Target Translations (main/i18n/Translation-en) is configured multiple times in /etc/apt/sources.list.d/php.list:1 and /etc/apt/sources.list.d/php7.list:1
请问我该如何解决这个问题？