testing/vlang: upgrade to 0.4.8

https://github.com/vlang/v/releases/tag/0.4.8
https://github.com/vlang/v/releases/tag/0.4.7
https://github.com/vlang/v/releases/tag/0.4.6
https://github.com/vlang/v/releases/tag/0.4.5
https://github.com/vlang/v/releases/tag/0.4.4
https://github.com/vlang/vc/commit/54beb1f416b404a06b894e6883a0e2368d80bc3e
https://github.com/vlang/vc/compare/5e691a8...54beb1f

Also resolves an -Wimplicit-function-declaration error in vc with musl and gcc 14.

vc/v.c: In function 'print_backtrace_skipping_top_frames_linux':
vc/v.c:21619:47: error: implicit declaration of function 'backtrace' [-Wimplicit-function-declaration]
21619 |                                 int nr_ptrs = backtrace(&buffer[0], 100);
      |                                               ^~~~~~~~~
vc/v.c:21626:51: error: implicit declaration of function 'backtrace_symbols' [-Wimplicit-function-declaration]
21626 |                                 char** csymbols = backtrace_symbols(((voidptr)(&buffer[v_fixed_index(skipframes, 100)])), nr_actual_frames);
      |                                                   ^~~~~~~~~~~~~~~~~
vc/v.c:21626:51: error: initialization of 'char **' from 'int' makes pointer from integer without a cast [-Wint-conversion]