remove unsupported board and change target branch

Signed-off-by: Masaya Kataoka <ms.kataoka@gmail.com>

Author: hakuturu583

.github/workflows/build.yaml

@@ -7,7 +7,7 @@ on:
   workflow_dispatch:
   push:
     branches:
-      - master
+      - main
 
 jobs:
   build:
@@ -20,7 +20,6 @@ jobs:
         - ARCH_MAX
         - DISCO_F746NG
         - DISCO_F769NI
-#        - DISCO_H747I comment out because of CI error.
         - GR_MANGO
         - NUCLEO_F429ZI
         - NUCLEO_F767ZI