kokoro linux: use 'lean' image based on ubuntu 24.04

dneto0 · dneto0 · commit dce5fb20a6e2 · 2025-01-29T13:22:39.000-05:00
diff --git a/kokoro/common.cfg b/kokoro/common.cfg
@@ -0,0 +1,4 @@
+env_vars {
+  key: "LINUX_BUILDER_IMAGE"
+  value: "us-east4-docker.pkg.dev/shaderc-build/radial-docker/radial-ubuntu-2404-amd64-lean"
+}
