fix(get_updates): ignore null update entries

[Gujiassh]

Summary

• treat all-null update arrays the same as an empty updates result instead of letting null entries fall through to formatting
• filter update rows before deciding whether to return the standard no-updates message
• add regression coverage for the nullable updates path

Testing

• npx jest src/core/tools/platform-api-tools/get-updates-tool/get-updates-tool.test.ts
• npx eslint src/core/tools/platform-api-tools/get-updates-tool/get-updates-tool.ts src/core/tools/platform-api-tools/get-updates-tool/get-updates-tool.test.ts
• npm run build