Renamed validation layers build (flutter/engine#42826)

followup to https://github.com/flutter/engine/pull/42724

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engine/src/flutter/ci/builders/linux_android_debug_engine.json

@@ -146,7 +146,7 @@
                 "--no-lto",
                 "--enable-vulkan-validation-layers"
             ],
-            "name": "android_debug_arm64",
+            "name": "android_debug_arm64_validation_layers",
             "ninja": {
                 "config": "android_debug_arm64",
                 "targets": [