Improve trailing version string error message (#3453)
We would previously show the parsed version when erroring due to
trailing content after a valid version, which can look different than
the input. E.g. when encountering `0.1-bulbasaur`, we would display:
```
after parsing '0.1b0', found 'ulbasaur', which is not part of a valid version
```
With storing the input string instead of the input version, we now show:
```
after parsing '0.1-b', found 'ulbasaur', which is not part of a valid version
```
