Fix rbt alias --dry-run with system command aliases.

Review Request #12194 — Created March 22, 2022 and submitted — Latest diff uploaded


When running rbt alias --dry-run on a system command alias (an alias
that executes a command, marked with a leading !), the result would be
a list of characters separated by spaces.

This was due to a bad assumption in the code where we assumed the value
we were working with was a list, each representing part of a command
invocation. These sorts of aliases were represented as a string, so we
ended up treating the string as a list of individual characters,
inserting spaces between each.

This change fixes this bug buy only attempting this normalization if
working with a list. Strings are printed as-is.

Tested with both types of aliases. Saw the expected results.

Tested the links in the new release notes.