ci: use arch:arm64 instead of runner:apm-k8s-arm-metal

- Replace unavailable runner tag with standard arch:arm64
- Project lacks access to apm-k8s-arm-metal runner pool

This commit made by [/dd:git:commit:quick](https://github.com/DataDog/claude-marketplace/tree/main/dd/commands/git/commit/quick.md)

Author: jbachorik

.gitlab/benchmarks/.gitlab-ci.yml

@@ -70,7 +70,7 @@ benchmarks-candidate-amd64:
 
 benchmarks-candidate-aarch64:
   extends: .benchmark_job
-  tags: ["runner:apm-k8s-arm-metal"]
+  tags: ["arch:arm64"]
   image: $BENCHMARK_IMAGE_ARM64
   variables:
     KUBERNETES_MEMORY_REQUEST: 200Gi

.gitlab/dd-trace-integration/.gitlab-ci.yml

@@ -221,7 +221,7 @@ integration-test-x64-musl:
 
 integration-test-arm64-glibc:
   extends: .integration_test_base
-  tags: [ "runner:apm-k8s-arm-metal" ]
+  tags: [ "arch:arm64" ]
   image: ${BUILD_IMAGE_ARM64}
   parallel:
     matrix:
@@ -235,7 +235,7 @@ integration-test-arm64-glibc:
 
 integration-test-arm64-musl:
   extends: .integration_test_base
-  tags: [ "runner:apm-k8s-arm-metal" ]
+  tags: [ "arch:arm64" ]
   image: ${BUILD_IMAGE_ARM64_MUSL}
   parallel:
     matrix: