fix: correct sidereal_day constant in astronomy.h (issue #786)

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Co-authored-by: mpusz <506260+mpusz@users.noreply.github.com>

Author: Copilot

src/systems/include/mp-units/systems/astronomy.h

@@ -40,7 +40,7 @@ namespace mp_units::astronomy {
 // clang-format off
 // time
 inline constexpr struct day final : named_unit<"D", non_si::day> {} day;
-inline constexpr struct sidereal_day final : named_unit<"D_sid", mag_ratio<86'164'0905, 1'000'000> * si::second> {} sidereal_day;
+inline constexpr struct sidereal_day final : named_unit<"D_sid", mag_ratio<861'640'905, 10'000> * si::second> {} sidereal_day;
 inline constexpr struct Julian_year final : named_unit<"a", mag_ratio<365'25, 100> * day> {} Julian_year;
 inline constexpr struct tropical_year final : named_unit<"a_trop", mag_ratio<365'242189, 1'000'000> * day> {} tropical_year;
 inline constexpr struct century final : named_unit<"c", mag<100> * Julian_year> {} century;