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

Also, use lightweight license-checker image

BUG=393622588,391948942

Author: dneto0

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"
+}

kokoro/license-check/presubmit-docker.sh

@@ -21,7 +21,6 @@ ROOT_DIR="$( cd "${SCRIPT_DIR}/../.." >/dev/null 2>&1 && pwd )"
 
 docker run --rm -i \
   --volume "${ROOT_DIR}:${ROOT_DIR}" \
-  --volume "${KOKORO_ARTIFACTS_DIR}:/mnt/artifacts" \
   --workdir "${ROOT_DIR}" \
-  --entrypoint "${SCRIPT_DIR}/presubmit-docker.sh" \
-  "gcr.io/shaderc-build/radial-build:latest"
+  --entrypoint /bin/license-checker \
+  us-east4-docker.pkg.dev/shaderc-build/radial-docker/ubuntu-24.04-amd64/license-checker

kokoro/license-check/presubmit.sh

@@ -29,4 +29,4 @@ docker run --rm -i \
   --env BUILD_TARGET_ARCH=$BUILD_TARGET_ARCH \
   --env BUILD_SANITIZER=$BUILD_SANITIZER \
   --entrypoint "${SCRIPT_DIR}/presubmit-docker.sh" \
-  "gcr.io/shaderc-build/radial-build:latest"
+  us-east4-docker.pkg.dev/shaderc-build/radial-docker/ubuntu-24.04-amd64/lean