Test large runners for Linux x86_64 (#333)

Extend the nightly build-and-test workflow to run on both arm64 and
x86_64 platforms. This change adds support for GitHub-hosted large
runners targeting Linux x86_64, allowing us to validate toolchain builds
across architectures.

This is part of an evaluation of GitHub’s large runners for Linux
workloads.

Author: HugoSilvaSantos

.github/workflows/atfe_nightly_build_and_test.yml

@@ -31,7 +31,7 @@ jobs:
         include:
           - build_script: build.sh
             test_script: test.sh
-            runner: ah-ubuntu_22_04-c7g_8x-100
+            runner: ToolchainGroup_LargeRunner_Linux-x64
           - build_script: build_llvmlibc_overlay.sh
             test_script: ''
             runner: ah-ubuntu_22_04-c7g_8x-100