update stm32 board manager url

Author: Richard Unger

.github/workflows/ccpp.yml

@@ -54,10 +54,10 @@ jobs:
             required-libraries: Simple FOC
             sketches-exclude: calibrated
           - arduino-boards-fqbn: STM32:stm32:GenF1:pnum=BLUEPILL_F103C8
-            platform-url: https://github.com/stm32duino/BoardManagerFiles/raw/master/STM32/package_stm_index.json 
+            platform-url:  https://github.com/stm32duino/BoardManagerFiles/raw/main/package_stmicroelectronics_index.json 
             required-libraries: Simple FOC
           - arduino-boards-fqbn: STM32:stm32:Nucleo_64:pnum=NUCLEO_F411RE
-            platform-url: https://github.com/stm32duino/BoardManagerFiles/raw/master/STM32/package_stm_index.json 
+            platform-url:  https://github.com/stm32duino/BoardManagerFiles/raw/main/package_stmicroelectronics_index.json 
             required-libraries: Simple FOC
       # Do not cancel all jobs / architectures if one job fails
       fail-fast: false