patcht6300: fix setup with GPGSSH but without GPG

>
> In a test introduced by 26c9c03f0a (ref-filter: add new "signature"
> atom, 2023-06-04) the file named "file" is added by a setup step that
> requires GPG and modified by a second setup step that requires GPGSSH.
> Systems lacking the first prerequisite skip the initial setup step and
> then "git commit -a" in the second one doesn't find the modified file.
> Add it explicitly.

> In a test introduced by 26c9c03f0a (ref-filter: add new "signature"
> atom, 2023-06-04) the file named "file" is added by a setup step that
> requires GPG and modified by a second setup step that requires GPGSSH.
> Systems lacking the first prerequisite skip the initial setup step and
> then "git commit -a" in the second one doesn't find the modified file.
> Add it explicitly.
>
> Signed-off-by: René Scharfe <l.s.r@web.de>
> ---
>  t/t6300-for-each-ref.sh | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)

> diff --git a/t/t6300-for-each-ref.sh b/t/t6300-for-each-ref.sh
> index 6e6ec852b5..1180c3254c 100755
> --- a/t/t6300-for-each-ref.sh
> +++ b/t/t6300-for-each-ref.sh
> @@ -1584,7 +1584,8 @@ test_expect_success GPGSSH 'setup for signature atom using ssh' '
>  	test_config user.signingkey "${GPGSSH_KEY_PRIMARY}" &&
>  	echo "8" >file &&
>  	test_tick &&
> -	git commit -a -S -m "file: 8" &&
> +	git add file &&
> +	git commit -S -m "file: 8" &&
>  	git tag eighth-signed-ssh
>  '
>
> --
> 2.41.0

> René Scharfe <l.s.r@web.de> writes:
>
>> In a test introduced by 26c9c03f0a (ref-filter: add new "signature"
>> atom, 2023-06-04) the file named "file" is added by a setup step that
>> requires GPG and modified by a second setup step that requires GPGSSH.
>> Systems lacking the first prerequisite skip the initial setup step and
>> then "git commit -a" in the second one doesn't find the modified file.
>> Add it explicitly.
>>
>> Signed-off-by: René Scharfe <l.s.r@web.de>
>> ---
>>  t/t6300-for-each-ref.sh | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> Thanks for good eyes.
>
> I guess a box without GPG is not so uncommon, and even such a box
> can reasonably be expected to have SSH on it, so I would believe if
> this was discovered on a real development box, but is that how you
> found this?  Or have you invented a nice test helper that lets you
> pick random set of prerequisites and try permutations of having and
> not having them, or something nice like that?