Remove Node.js less than 18.19.0 support

[ybiquitous]

Which issue, if any, is this issue related to?

None.

Is there anything in the PR that needs further explanation?

The npx ls-engines command reports as below:

Your “engines” field allows more node versions than your dependency graph does.

┌──────────────────────────────┬──────────────────────┐
│ Conflicting dependencies (2) │ engines.node         │
├──────────────────────────────┼──────────────────────┤
│ execa                        │ ^18.19.0 || >=20.5.0 │
├──────────────────────────────┼──────────────────────┤
│ human-signals                │ >=18.18.0            │
└──────────────────────────────┴──────────────────────┘

[ybiquitous]

Node.js v18 has been in maintenance, so I think there is no problem with dropping the support of <18.19.0.
See https://nodejs.org/en/about/previous-releases