RFC: make promote throw an error if no arguments can be changed

[JeffBezanson]

Fixes #22801.

[lostanlen]

The use of a comma in the NEWS.md entry
"The promote function now raises an error if its arguments are of different types, and attempting to convert them to a common type fails to change any of their types."
changes the logical meaning of the sentence.

I think it would be best to remove the comma and repeat the conjunction "if".
"The promote function now raises an error if its arguments are of different types and if attempting to convert them to a common type fails to change any of their types."

[JeffBezanson]

@nanosoldier runbenchmarks(ALL, vs=":master")

[nanosoldier]

Your benchmark job has completed - possible performance regressions were detected. A full report can be found here. cc @ararslan