Include executable file and license inside a directory during release

[MatteoPologruto]

Previously, the release system generated archives without a root folder:

$ wget https://downloads.arduino.cc/tools/arduinoOTA/arduinoOTA_1.4.0_macOS_64bit.tar.gz

[...]

$ tar -t -f arduinoOTA_1.4.0_macOS_64bit.tar.gz 

arduinoOTA
LICENSE.txt

Arduino Boards Manager requires tool dependency archives to contain a root folder, so the lack of one caused installations of dependent platforms to fail:

Downloading packages
arduino:arduinoOTA@1.4.0
arduino:megaavr@1.8.8
Installing arduino:arduinoOTA@1.4.0
Failed to install platform: arduino:megaavr.
Error: 13 INTERNAL: Cannot install tool arduino:arduinoOTA@1.4.0: searching package root dir: files in archive must be placed in a subdirectory

The changes proposed here will result in release archives which do contain the required root folder:

$ tar -t -f arduinoOTA_8.8.8_macOS_64bit.tar.gz 

arduinoOTA_osx_darwin_amd64/
arduinoOTA_osx_darwin_amd64/arduinoOTA
arduinoOTA_osx_darwin_amd64/LICENSE.txt

Test release: https://github.com/MatteoPologruto/arduinoOTA/releases/tag/8.8.8