patchGitHub CI: macos-13 images are no more

> As this image was deprecated on Sep 22nd, and will be dropped on Dec
> 4th, replace these jobs to use macos-14 images instead.
>
> Signed-off-by: Junio C Hamano <gitster@pobox.com>
> ---
>
>  * This is a monkey-see-monkey-do patch.  There may be additional
>    adjustment necessary (versions of tools available on the system
>    may be different, for example).

>  .github/workflows/main.yml | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
> index aa6bce673b..f2af90ad31 100644
> --- a/.github/workflows/main.yml
> +++ b/.github/workflows/main.yml
> @@ -313,16 +313,16 @@ jobs:
>          vector:
>            - jobname: osx-clang
>              cc: clang
> -            pool: macos-13
> +            pool: macos-14
>            - jobname: osx-reftable
>              cc: clang
> -            pool: macos-13
> +            pool: macos-14
>            - jobname: osx-gcc
>              cc: gcc-13
> -            pool: macos-13
> +            pool: macos-14
>            - jobname: osx-meson
>              cc: clang
> -            pool: macos-13
> +            pool: macos-14
>      env:
>        CC: ${{matrix.vector.cc}}
>        CC_PACKAGE: ${{matrix.vector.cc_package}}

> Junio C Hamano <gitster@pobox.com> writes:
> 
> > As this image was deprecated on Sep 22nd, and will be dropped on Dec
> > 4th, replace these jobs to use macos-14 images instead.
> >
> > Signed-off-by: Junio C Hamano <gitster@pobox.com>
> > ---
> >
> >  * This is a monkey-see-monkey-do patch.  There may be additional
> >    adjustment necessary (versions of tools available on the system
> >    may be different, for example).
> 
> This, when test-merged to 'master' and also to 'next', seems to be
> enough to get GitHub Actions based CI pass.  I'll fast-track it in
> order to allow us to run it with the upcoming -rc1, and eventually
> down to 'maint',