Fix default value of stdin with $

[ehmicky]

Fixes #549

This makes stdin of processes created with $ default to inherit instead of pipe, as this is most likely the intended behavior of users in that case.

This is technically a breaking change from 7.1.0. However, considering this is a very recent release and this is correcting the intended behavior, I am not sure whether we can consider 7.1.0's behavior a bug, i.e. this would be a bug fix instead? 🤔

[ehmicky]

I think $.sync is implied by $, so I am not sure we need to be explicit there.

[sindresorhus]

This is technically a breaking change from 7.1.0. However, considering this is a very recent release and this is correcting the intended behavior, I am not sure whether we can consider 7.1.0's behavior a bug, i.e. this would be a bug fix instead?

I would see it as a bug-fix.

[sindresorhus]

Can you fix the merge conflict? Feel free to merge and release afterwards.

[yuri-scarbaci-lenio]

Just for the record,
this isn't only "technically" a breaking change,
this did actually have an impact in our implementation,

we have a scenario in which we use husky & wdio to run e2e test on a pre-push commit,
long story short:
wdio checks for the isTTY flag and makes an assumption based on that on the format of the piped-in values
husky/git pre-push hook are piping in "references"
execa change ( as expected but also in a breaking way) pipes in the "references" in stdin and that causes the flow we had to break

the change on our side was just clearly defining the flags for execa as

  {
     stdin: 'ignore',
     stdout: 'inherit',
     stderr: 'inherit',
   },

and this would bring the behaviour back to what we where previously doing before this PR was merged
(to be clear, in our own implementation we didn't expect any pipe-in at all from stdin, that's why the flag we used is ignore, in your case you may need to use pipe or handle it in some other way)

Leaving this here just for if anyone else is affected

some references:
https://git-scm.com/docs/githooks#_pre_push
https://github.com/webdriverio/webdriverio/blob/4cad54447a51d960914851477d365c29087791dd/packages/wdio-cli/src/commands/run.ts#L211