(node) upgrade node to 20.12.2

looks like the vulnerability is only windows-related, but upgrading from v18 to v20 shows a small performance increase (at least on my machine, CI does not agree ☹).

improvements to run-wrapper:

• calls pnpm in case no bin file is found (e.g. for run-file)
• uses exec to replace shell, so that no additional child process is created
• cds into the repository in case relative files are referenced

not yet tested on test

there could be a problem due to some dependencies being compiled and being incompatible between node versions (need to further research whether this is solvable or whether we risk a all-locales-temporarily-down scenario). I am also fine with leaving it at v18 for now and just changing the run wrapper for now