[ci] [R-package] test against R 4.3 on Windows

[jameslamb]

Contributes to #3756.

Moves all R 4.x CI jobs to R 4.3.1 (the latest available version).

Issues this PR's changes address

On Windows (minGW)

* checking whether package 'lightgbm' can be installed ... [222s] WARNING

Found the following significant warnings:

  src\external_libs\fmt\include\fmt\core.h:2042:48: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]

See 'D:/a/LightGBM/LightGBM/lightgbm.Rcheck/00install.out' for details.

This did not show up on R 4.2. It seems related to fmtlib/fmt#3533, and seems to have been fixed by updated fmt in #6074.

On Windows (MSVC)

D:\a\LightGBM\LightGBM\RLibrary\R\include\R_ext/Complex.h(81,21): error C3646: 'private_data_c': unknown override specifier (compiling source file C:\Users\runneradmin\RtmpiGO4kB\Rbuild10684dd767b0\lightgbm\src\src\lightgbm_R.cpp)

Looks like this is caused by this change to include/R_ext/Complex.h in R's headers, here: wch/r-source@fb52ac1. And from that commit, seems that the R Core team understood that this was something that not all compilers might support:

/* This definition uses an anonymous structure, which is defined in C11 (but
not C99).  It is, however, supported at least by GCC, clang and icc.  The
private_data_c member should never be used in code, but tells the compiler
about type punning when accessing the .r and .i elements, so is safer to use
when interfacing with Fortran COMPLEX*16 or directly C99 _Complex double
(PR#18430).

This form of static initialization works with both definitions:
Rcomplex z = { .r = 1, .i = 2 }; */

typedef union {
    struct {
	double r;
	double i;
    };
    double _Complex private_data_c;
} Rcomplex;

Seems to be that MSVC does not like anonymous types in structs: https://stackoverflow.com/a/58571593/3986677.

[jameslamb]

@guolinke could you please review this when you have time?

[jameslamb]

thank you!

[github-actions]

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