pub fn values_mut(&mut self) -> ValuesMut<'_> {
        ValuesMut {
            inner: self.headers.iter_mut(),
        }
    }
An iterator visiting all values mutably.

The iteration order is arbitrary, but consistent across platforms for
the same crate version.

# Examples

```
# use tonic::metadata::*;
let mut map = MetadataMap::default();

map.insert("x-word", "hello".parse().unwrap());
map.append("x-word", "goodbye".parse().unwrap());
map.insert("x-number", "123".parse().unwrap());

for value in map.values_mut() {
match value {
ValueRefMut::Ascii(mut value) =>
value.set_sensitive(true),
ValueRefMut::Binary(mut value) =>
value.set_sensitive(false),
}
}
```
tonic/src/metadata/map.rs