Add self hosted runners (#309)

- The runners are hosted and maintained by Arm
- c7g.8xlarge
- Ubuntu 22.04

Author: HugoSilvaSantos

.github/workflows/atfe_nightly_build_and_test.yml

@@ -31,16 +31,16 @@ jobs:
         include:
           - build_script: build.sh
             test_script: test.sh
-            runner: ubuntu-22.04
+            runner: ah-ubuntu_22_04-c7g_8x-100
           - build_script: build_llvmlibc_overlay.sh
             test_script: ''
-            runner: ubuntu-22.04
+            runner: ah-ubuntu_22_04-c7g_8x-100
           - build_script: build_newlib_nano_overlay.sh
             test_script: ''
-            runner: ubuntu-22.04
+            runner: ah-ubuntu_22_04-c7g_8x-100
           - build_script: build_newlib_overlay.sh
             test_script: ''
-            runner: ubuntu-22.04
+            runner: ah-ubuntu_22_04-c7g_8x-100
 
     steps:
       - name: Checkout