turndown-plugin-gfm: Fixes #10328 fix compatibility with turndown

[rrgeorge]

Fixes #10328 as recommended by @flaviut to maintain compatibility with turndown

[github-actions]

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[laurent22]

Doesn't build

2024-08-26T05:05:54.5809490Z ➤ YN0000: │ root@workspace:. STDOUT ➤ YN0000: [@joplin/turndown-plugin-gfm]: src/gfm.js → lib/turndown-plugin-gfm.cjs.js...
2024-08-26T05:05:54.6079490Z ➤ YN0000: │ root@workspace:. STDOUT ➤ YN0000: [@joplin/turndown-plugin-gfm]: [!] Error: Unexpected token
2024-08-26T05:05:54.6083270Z ➤ YN0000: │ root@workspace:. STDOUT ➤ YN0000: [@joplin/turndown-plugin-gfm]: src/tables.js (182:41)
2024-08-26T05:05:54.6151080Z ➤ YN0000: │ root@workspace:. STDOUT ➤ YN0000: [@joplin/turndown-plugin-gfm]: 180:   for (let i = 0; i < node.childNodes.length; i++) {
2024-08-26T05:05:54.6184020Z ➤ YN0000: │ root@workspace:. STDOUT ➤ YN0000: [@joplin/turndown-plugin-gfm]: 181:     const child = node.childNodes[i];
2024-08-26T05:05:54.6207870Z ➤ YN0000: │ root@workspace:. STDOUT ➤ YN0000: [@joplin/turndown-plugin-gfm]: 182:     if (types === 'code' && isCodeBlock_?.(child)) return true;
2024-08-26T05:05:54.6217470Z ➤ YN0000: │ root@workspace:. STDOUT ➤ YN0000: [@joplin/turndown-plugin-gfm]:                                               ^
2024-08-26T05:05:54.6225630Z ➤ YN0000: │ root@workspace:. STDOUT ➤ YN0000: [@joplin/turndown-plugin-gfm]: 183:     if (types.includes(child.nodeName)) return true;
2024-08-26T05:05:54.6277060Z ➤ YN0000: │ root@workspace:. STDOUT ➤ YN0000: [@joplin/turndown-plugin-gfm]: 184:     if (nodeContains(child, types)) return true;
2024-08-26T05:05:54.6282040Z ➤ YN0000: │ root@workspace:. STDOUT ➤ YN0000: [@joplin/turndown-plugin-gfm]:
2024-08-26T05:05:54.6283960Z ➤ YN0000: │ root@workspace:. STDOUT ➤ YN0000: [@joplin/turndown-plugin-gfm]: Process exited (exit code 1), completed in 0s 984ms

[flaviut]

weird that it doesn't compile, optional chaining has been a standard JS feature since 2020.

Should be easy enough to change (I can't sign that CLA though and do it myself)