fix missing initializer 'rot' warning

[yani]

I came across this warning:

deps/astronomy/astronomy.c: In function ‘Astronomy_Constellation’:
deps/astronomy/astronomy.c:11233:5: warning: missing initializer for field ‘rot’ of ‘astro_rotation_t’ [-Wmissing-field-initializers]
11233 |     static astro_rotation_t rot = { ASTRO_NOT_INITIALIZED };
      |     ^~~~~~
In file included from deps/astronomy/astronomy.c:45:
deps/astronomy/astronomy.h:527:12: note: ‘rot’ declared here
  527 |     double rot[3][3];       /**< A normalized 3x3 rotation matrix. */
      |            ^~~

Changing line 11233 to:

static astro_rotation_t rot = { ASTRO_NOT_INITIALIZED, {{0}} };

Fixes the warning.