exec should not fail if provided a command with a missing tool when using {ignoreReturnCode: true, failOnStdErr:false}

Describe the bug
I would expect that exec.exec('someCommandThatDoesNotExists', [], {ignoreReturnCode:true, failOnStdErr:false}) would simply return a Promise that resolves to 127.
Instead it appears that it throws an exception: which ultimately comes from the fact that it is using io.which with a check flag equal to true over at https://github.com/actions/toolkit/blob/main/packages/exec/src/toolrunner.ts#L411

To Reproduce
Steps to reproduce the behavior:
From a custom javascript based github action perform
const exitCode = await exec.exec('someCommandThatDoesNotExists', [], {ignoreReturnCode:true, failOnStdErr:false})
and a execute the action

Expected behavior
You'll find that instead of getting the exitCode to process yourself, an exception is thrown. This is not at all what is expected from users like myself when I explicitly requested to process the return code myself with
ignoreReturnCode:true, failOnStdErr:false

A Promise that resolves to 127 should be returned.

Desktop (please complete the following information):
all platforms

Start at packages/exec/src/toolrunner.ts around line 411, where io.which is called with check enabled, and reproduce the issue from a custom JavaScript GitHub Action using exec.exec with both options. Done means a missing command resolves with exit code 127 instead of throwing when ignoreReturnCode is true and failOnStdErr is false.