Update aarch64 to GCC 11 (rapidsai#978)

This PR updates aarch64 dependencies to use GCC 11. Follow-up to rapidsai#961.

Authors:
  - Bradley Dice (https://github.com/bdice)

Approvers:
  - Mark Harris (https://github.com/harrism)
  - AJ Schmidt (https://github.com/ajschmidt8)

URL: rapidsai#978

dependencies.yaml

@@ -70,7 +70,7 @@ dependencies:
           - matrix:
               arch: aarch64
             packages:
-              - &gcc_aarch64 gcc_linux-aarch64=9.*
+              - &gcc_aarch64 gcc_linux-aarch64=11.*
               - &sysroot_aarch64 sysroot_linux-aarch64==2.17
       - output_types: conda
         matrices: