add env [tasmota3] -> Tasmota build with core 3.0.x stage

[Jason2866]

Description:

using toolchain with fix for esp8266/Arduino#8393

Checklist:

• The pull request is done against the latest development branch
• Only relevant files were touched
• Only one feature/fix was added per PR and the code change compiles without warnings
• The code change is tested and works with Tasmota core ESP8266 V.2.7.4.9
• The code change is tested and works with Tasmota core ESP32 V.2.0.1.1
• I accept the CLA.

NOTE: The code change must pass CI tests. Your PR cannot be merged unless tests pass