re-enable flang-21 on aarch64

Author: mayeut

.github/workflows/dynamic_arch.yml

@@ -32,9 +32,6 @@ jobs:
             fortran: flang
           - fortran: flang-21
             cc: clang
-          # flang-21 fails on aarch64
-          - os: linux-aarch64
-            fortran: flang-21
 
     steps:
       - name: Checkout repository