fix(plugin-js-packages): handle empty output from yarn outdated

[matejchalk]

Fixes error in for Yarn v1 repo where there are no outdated packages, so yarn oudated --json doesn't print any JSON lines.

[ warn ] Plugins failed: 
[ warn ] Error: - Plugin JS Packages (js-packages) produced the following error:
  - file:///REDACTED/node_modules/@code-pushup/js-packages-plugin/src/lib/package-managers/yarn-classic/outdated-result.js:6
    const fields = yarnv1Outdated[1].data.head;
                                     ^
TypeError: Cannot read properties of undefined (reading 'data')
    at Object.yarnv1ToOutdatedResult [as unifyResult] (file:///REDACTED/node_modules/@code-pushup/js-packages-plugin/src/lib/package-managers/yarn-classic/outdated-result.js:6:38)
    at processOutdated (file:///REDACTED/node_modules/@code-pushup/js-packages-plugin/src/lib/runner/index.js:47:42)
    at async executeRunner (file:///REDACTED/node_modules/@code-pushup/js-packages-plugin/src/lib/runner/index.js:28:11)
    at async file:///REDACTED/node_modules/@code-pushup/js-packages-plugin/src/bin.js:5:1
Node.js v22.14.0

[github-actions]

Code PushUp

🤨 Code PushUp report has both improvements and regressions – compared current commit 6c8c4ca with previous commit bf33ffa.

🕵️ See full comparison in Code PushUp portal 🔍

🏷️ Categories

🏷️ Category	⭐ Previous score	⭐ Current score	🔄 Score change
Performance	🟡 52	🔴 49
Code coverage	🟢 90	🟢 90
Security	🟡 67	🟡 67	–
Updates	🟡 81	🟡 81	–
Accessibility	🟢 92	🟢 92	–
Best Practices	🟢 100	🟢 100	–
SEO	🟡 61	🟡 61	–
Type Safety	🟢 100	🟢 100	–
Bug prevention	🟢 100	🟢 100	–
Miscellaneous	🟢 100	🟢 100	–
Code style	🟢 100	🟢 100	–
Documentation	🔴 23	🔴 23	–

👎 2 groups regressed, 👍 1 audit improved, 👎 5 audits regressed, 15 audits changed without impacting score

🗃️ Groups

🔌 Plugin	🗃️ Group	⭐ Previous score	⭐ Current score	🔄 Score change
Lighthouse	Performance	🟡 52	🔴 49
Code coverage	Code coverage metrics	🟢 90	🟢 90

19 other groups are unchanged.

🛡️ Audits

🔌 Plugin	🛡️ Audit	📏 Previous value	📏 Current value	🔄 Value change
Lighthouse	First Contentful Paint	🟨 2.7 s	🟥 3.1 s
Lighthouse	Speed Index	🟥 5.9 s	🟥 6.4 s
Lighthouse	Largest Contentful Paint	🟨 3.5 s	🟨 3.7 s
Lighthouse	Time to Interactive	🟥 12.5 s	🟥 12.9 s
Lighthouse	Total Blocking Time	🟥 3,870 ms	🟥 3,350 ms
Code coverage	Branch coverage	🟨 86 %	🟨 86 %
Lighthouse	Avoids enormous network payloads	🟩 Total size was 1,838 KiB	🟩 Total size was 1,839 KiB
Lighthouse	Metrics	🟩 100%	🟩 100%
Lighthouse	JavaScript execution time	🟥 5.6 s	🟥 5.9 s
Lighthouse	Minimizes main-thread work	🟥 15.3 s	🟥 15.1 s
Lighthouse	Uses efficient cache policy on static assets	🟨 28 resources found	🟨 28 resources found
Lighthouse	Max Potential First Input Delay	🟥 1,560 ms	🟥 1,700 ms
Lighthouse	Eliminate render-blocking resources	🟥 Potential savings of 810 ms	🟥 Potential savings of 690 ms
Lighthouse	Initial server response time was short	🟩 Root document took 430 ms	🟩 Root document took 520 ms
Lighthouse	Server Backend Latencies	🟩 310 ms	🟩 360 ms
Lighthouse	Network Round Trip Times	🟩 20 ms	🟩 60 ms
Lighthouse	Reduce unused CSS	🟥 Potential savings of 67 KiB	🟥 Potential savings of 67 KiB
JS Packages	Outdated NPM dev dependencies.	🟨 52 outdated package versions (27 major, 19 minor, 6 patch)	🟨 53 outdated package versions (27 major, 19 minor, 6 patch, 1 prerelease)
Lighthouse	Avoid large layout shifts	🟩 0	🟩 1 layout shift found
Lighthouse	Avoids an excessive DOM size	🟥 2,167 elements	🟥 2,166 elements
Lighthouse	Cumulative Layout Shift	🟩 0	🟩 0.002

582 other audits are unchanged.