fix(dev-tool): resolve no-useless-assignment error under ESLint v10

ESLint v10's eslint:recommended enables the new no-useless-assignment
rule. dev-tool uses a standalone eslint.config.mjs that applies
@eslint/js recommended directly, so the warn-downgrade in the shared
eslint-customized.ts config does not reach it and the rule fires as an
error. Drop the redundant '= undefined' initializer on artifactURL
(every code path reassigns or throws before it is read).

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Copilot-Session: cf6320ed-d2d6-420c-8188-6a63a557ca4b

Author: jeremymeng

common/tools/dev-tool/src/commands/samples/checkNodeVersions.ts

@@ -149,7 +149,7 @@ async function createDockerContextDirectory(
   }
   const envFileName = path.basename(envPath);
   await cp(samplesPath, path.join(dockerContextDirectory, "samples"), { recursive: true });
-  let artifactURL: string | undefined = undefined;
+  let artifactURL: string | undefined;
   try {
     await access(artifactPath);
     const artifactName = path.basename(artifactPath);