CI-testing a fix for the "ambiguous conversion" issue.

This change is known to fix the `tensorflow::tstring` issue reported under #3521 (comment)

TODO: Minimal reproducer for the `tensorflow::tstring` issue.

include/pybind11/pytypes.h

@@ -1185,8 +1185,10 @@ class bytes : public object {
     }
 
 #ifdef PYBIND11_HAS_STRING_VIEW
+    // enable_if is needed to avoid "ambiguous conversion" errors (see PR #3521).
     // NOLINTNEXTLINE(google-explicit-constructor)
-    bytes(std::string_view s) : bytes(s.data(), s.size()) { }
+    template <typename T, detail::enable_if_t<std::is_same<T, std::string_view>::value, int> = 0>
+    bytes(T s) : bytes(s.data(), s.size()) { }
 
     // Obtain a string view that views the current `bytes` buffer value.  Note that this is only
     // valid so long as the `bytes` instance remains alive and so generally should not outlive the