Fix comment in variant.h to refer to `absl::variant`.

The comment is updated to accurately reflect that `absl::variant` was the polyfill and is now an alias for `std::variant`.

PiperOrigin-RevId: 919336725
Change-Id: If39bd3f61f229f561d547391ca97015688b1fad1

absl/types/variant.h

diff --git a/absl/types/variant.h b/absl/types/variant.h
index 49f3e24..89ff8dd 100644
--- a/absl/types/variant.h
+++ b/absl/types/variant.h
@@ -16,9 +16,9 @@
 // variant.h
 // -----------------------------------------------------------------------------
 //
-// Historical note: Abseil once provided an implementation of `std::variant`
+// Historical note: Abseil once provided an implementation of `absl::variant`
 // as a polyfill for `std::variant` prior to C++17. Now that C++17 is required,
-// `std::variant` is an alias for `std::variant`.
+// `absl::variant` is an alias for `std::variant`.
 
 #ifndef ABSL_TYPES_VARIANT_H_
 #define ABSL_TYPES_VARIANT_H_