Upgrade Arm toolchain to 9-2020-q2

Because MCUBoot doesn't boot

.github/workflows/main.yml

@@ -117,7 +117,7 @@ jobs:
       uses: fiam/arm-none-eabi-gcc@v1.0.2
       with:
         # GNU Embedded Toolchain for Arm release name, in the V-YYYY-qZ format (e.g. "9-2019-q4")
-        release: 8-2019-q3
+        release: 9-2020-q2
         # Directory to unpack GCC to. Defaults to a temporary directory.
         directory: ${{ runner.temp }}/arm-none-eabi
 
@@ -206,4 +206,4 @@ jobs:
         find bin/targets/nrf52_my_sensor/app/apps/my_sensor_app -name "my_sensor_app.*" -ls
       
 # Embedded Arm Toolchain will only be cached if the build succeeds.
-# So make sure that the first build always succeeds, e.g. comment out the "Build" step.
+# So make sure that the first build always succeeds, e.g. comment out the "Build" step.