t7004: do not create unneeded gpghome/gpg.conf when GPG is not used

These tests themselves are properly protected by the GPG
prerequisite, but one of the set-up steps outside the
test_expect_success block unconditionally assumed that there is a
gpghome/ directory, which is not true if GPG is not being used.

It may be a good idea to move the whole set-up steps in the test but
that is a follow-up topic.
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

t/t7004-tag.sh

@@ -1066,12 +1066,12 @@ test_expect_success GPG \
 '
 
 # usage with rfc1991 signatures
-echo "rfc1991" > gpghome/gpg.conf
 get_tag_header rfc1991-signed-tag $commit commit $time >expect
 echo "RFC1991 signed tag" >>expect
 echo '-----BEGIN PGP MESSAGE-----' >>expect
 test_expect_success GPG \
 	'creating a signed tag with rfc1991' '
+	echo "rfc1991" >gpghome/gpg.conf &&
 	git tag -s -m "RFC1991 signed tag" rfc1991-signed-tag $commit &&
 	get_tag_msg rfc1991-signed-tag >actual &&
 	test_cmp expect actual
@@ -1085,6 +1085,7 @@ chmod +x fakeeditor
 
 test_expect_success GPG \
 	'reediting a signed tag body omits signature' '
+	echo "rfc1991" >gpghome/gpg.conf &&
 	echo "RFC1991 signed tag" >expect &&
 	GIT_EDITOR=./fakeeditor git tag -f -s rfc1991-signed-tag $commit &&
 	test_cmp expect actual
@@ -1092,11 +1093,13 @@ test_expect_success GPG \
 
 test_expect_success GPG \
 	'verifying rfc1991 signature' '
+	echo "rfc1991" >gpghome/gpg.conf &&
 	git tag -v rfc1991-signed-tag
 '
 
 test_expect_success GPG \
 	'list tag with rfc1991 signature' '
+	echo "rfc1991" >gpghome/gpg.conf &&
 	echo "rfc1991-signed-tag RFC1991 signed tag" >expect &&
 	git tag -l -n1 rfc1991-signed-tag >actual &&
 	test_cmp expect actual &&