Boards Manager installation of 2.8.1 release fails due to unsupported platform archive structure

The platform archive for the 2.8.1 release has an unsupported structure. This causes installation to fail when using the Arduino IDE 2.x or Arduino CLI Boards Manager:

Failed to install platform: Seeeduino:mbed.
Error: 13 INTERNAL: Cannot install platform: installing platform Seeeduino:mbed@2.8.1: searching package root dir: no unique root dir in archive, found 'C:\Users\per\AppData\Local\Arduino15\tmp\package-3860729226\.github' and 'C:\Users\per\AppData\Local\Arduino15\tmp\package-3860729226\bootloaders'

As indicated by the error, the problem is there is no root folder in the archive:

https://files.seeedstudio.com/arduino/core/mbed/ArduinoCore-mbed-Seeed-2.8.1.tar.gz

.
├── README.md
├── bfg_nano33ble.sh
├── boards.txt
├── bootloaders/
├── cores/
├── drivers/
├── edge.variables
├── extras/
├── full.variables
├── libraries/
├── mbed-os-to-arduino
├── mbed_lib.json
├── nano.variables
├── nicla.variables
├── package.sh
├── package_full.sh
├── patches/
├── platform.txt
├── portenta.variables
├── post_install.bat*
├── post_install.sh
├── programmers.txt
├── rp2040.variables
├── sketches-reports/
├── tools/
└── variants/

The platform archive of the 2.7.2 release has the correct structure:

https://files.seeedstudio.com/arduino/core/mbed/20220720_XIAOBLE_2.7.2.tar.bz2

.
└── 2.7.2/
    ├── README.md
    ├── bfg_nano33ble.sh
    ├── boards.txt
    ├── bootloaders/
    ├── cores/
    ├── drivers/
    ├── edge.variables
    ├── extras/
    ├── full.variables
    ├── libraries/
    ├── mbed-os-to-arduino
    ├── mbed_lib.json
    ├── nano.variables
    ├── nicla.variables
    ├── package.sh
    ├── package_full.sh
    ├── patches/
    ├── platform.txt
    ├── portenta.variables
    ├── post_install.bat*
    ├── post_install.sh
    ├── programmers.txt
    ├── rp2040.variables
    ├── tools/
    └── variants/

Originally reported at:

Seeed-Studio / ArduinoCore-mbed

Boards Manager installation of 2.8.1 release fails due to unsupported platform archive structure #14