Fix a typo of absl::Nonnull in the example comment.

PiperOrigin-RevId: 546897533
Change-Id: I3ad12f252c49e4672a64d00d0107111fdc5b6ac8

absl/base/nullability.h

@@ -164,7 +164,7 @@ namespace absl {
 // Example:
 //
 // // `employee` is designated as not null.
-// void PaySalary(absl::NotNull<Employee *> employee) {
+// void PaySalary(absl::Nonnull<Employee *> employee) {
 //   pay(*employee);  // OK to dereference
 // }
 template <typename T>