Reset matrix_need_update properly in eager debouncing algorithms (#21154)

The `matrix_need_update` variable needs to be reset to `false` in
`transfer_matrix_values()`, otherwise that function continues to be
invoked for every scanning loop (forever with `sym_eager_pk` and
`sym_eager_pk`, or until some key gets released with
`asym_eager_defer_pk`), and the scanning rate gets much lower because of
all that useless work.

Co-authored-by: Sergey Vlasov <sigprof@gmail.com>

quantum/debounce/sym_eager_pk.c

@@ -125,6 +125,7 @@ static void update_debounce_counters(uint8_t num_rows, uint8_t elapsed_time) {
 
 // upload from raw_matrix to final matrix;
 static void transfer_matrix_values(matrix_row_t raw[], matrix_row_t cooked[], uint8_t num_rows) {
+    matrix_need_update                   = false;
     debounce_counter_t *debounce_pointer = debounce_counters;
     for (uint8_t row = 0; row < num_rows; row++) {
         matrix_row_t delta        = raw[row] ^ cooked[row];