For some reason, the env vars are set correctly without refering the variable in `matrix` case-sensitvely:
```
2023-08-01T05:05:58.4626090Z env:
2023-08-01T05:05:58.4626367Z AR: arm-linux-gnueabihf-ar
2023-08-01T05:05:58.4626690Z CHOST: arm-linux-gnueabihf
2023-08-01T05:05:58.4626961Z CC: arm-linux-gnueabihf-gcc
2023-08-01T05:05:58.4627332Z CPP: arm-linux-gnueabihf-cpp
2023-08-01T05:05:58.4627662Z CXX: arm-linux-gnueabihf-g++
```
For clarify, we update them to match the definitions. Besides, `CXX` is
not needed and removed.