Fix unused variable warning in GCC7

PiperOrigin-RevId: 853321697
Change-Id: I44b09e10e6ca1bb9b9f30a01a0f5acd5923371c1

absl/strings/internal/str_format/float_conversion.cc

diff --git a/absl/strings/internal/str_format/float_conversion.cc b/absl/strings/internal/str_format/float_conversion.cc
index 0168662..bcef275 100644
--- a/absl/strings/internal/str_format/float_conversion.cc
+++ b/absl/strings/internal/str_format/float_conversion.cc
@@ -1745,7 +1745,7 @@
         bool change_to_zeros = false;
         if (nines + 1 >= digits_to_go) {
           // Everything we need to print is in the first DigitRun
-          auto [next_digit_opt, next_nines] = GetDigits(btd, digits_view);
+          auto next_digit_opt = GetDigits(btd, digits_view).digit;
           if (nines == state.precision) {
             change_to_zeros = next_digit_opt.value_or(0) > 4;
           } else {
@@ -1793,7 +1793,7 @@
             digits_to_go -= curr_nines + 1;
           } else {
             bool need_round_up = false;
-            auto [next_digit_opt, next_nines] = GetDigits(btd, digits_view);
+            auto next_digit_opt = GetDigits(btd, digits_view).digit;
             if (digits_to_go == 1) {
               need_round_up = curr_nines > 0 || next_digit_opt > 4;
             } else if (digits_to_go == curr_nines + 1) {