[range.split] Fix invalid conversion in example (#6041)

Replaces an illegal implicit conversion from a range to string_view
in the example with an explicit one.

After P2499R0, it is no longer possible to implicitly construct a
string_view from a range (like the ones produced by views::split).

Author: dangelog

source/ranges.tex

@@ -8146,8 +8146,8 @@
 \begin{example}
 \begin{codeblock}
 string str{"the quick brown fox"};
-for (string_view word : views::split(str, ' ')) {
-  cout << word << '*';
+for (auto word : views::split(str, ' ')) {
+  cout << string_view(word) << '*';
 }
 // The above prints \tcode{the*quick*brown*fox*}
 \end{codeblock}