FIX 'which' check in 'sake' now works for aliases

Description

sake may wrongly exit early on its which check, since the current implementation does the following:

This solution is problematic since the returned information string may include alias information (and more), which test -x can not interpret.

Additionally is the test -x check unnecessary since command -v already only returns executable command or fails if the command can not be found.

Therefore, I changed the source to just check for the exit status of command -v.

Run vendor/bin/sake dev/build on a POSIX compliant system, where which itself has been aliased.

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[x] The commit messages follow our commit message guidelines
[x] The PR follows our contribution guidelines
[x] Code changes follow our coding conventions
[x] This change is covered with tests (or tests aren't necessary for this change)
[x] Any relevant User Help/Developer documentation is updated; for impactful changes, information is added to the changelog for the intended release
[x] CI is green