t9350: skip ISO-8859-1 test when the environment is always-UTF-8

In the BusyBox-w32 version that is currently under consideration for
MinGit for Windows (to reduce the .zip size, and to avoid problems with
the MSYS2 runtime), the UTF-16 environment present in Windows is
considered to be authoritative, and the 8-bit version is always in UTF-8
encoding.

As a consequence, the ISO-8859-1 test in t9350-fast-export (which tries
to set GIT_AUTHOR_NAME to a ISO-8859-1 encoded value) *must* fail in
that setup.

So let's detect when it would fail (due to an environment being purely
kept UTF-8 encoded), and skip that test in that case.

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

t/t9350-fast-export.sh

@@ -94,6 +94,11 @@ test_expect_success 'fast-export --show-original-ids | git fast-import' '
 	test $MUSS = $(git rev-parse --verify refs/tags/muss)
 '
 
+test_lazy_prereq UTF8_ONLY_ENV '
+	. "$TEST_DIRECTORY"/t3901/8859-1.txt &&
+	! git var GIT_AUTHOR_IDENT | grep "Áéí"
+'
+
 test_expect_success 'reencoding iso-8859-7' '
 
 	test_when_finished "git reset --hard HEAD~1" &&
@@ -168,6 +173,10 @@ test_expect_success 'encoding preserved if reencoding fails' '
 		 test 252 -eq "$(git cat-file -s i18n-invalid)")
 '
 
+# The subsequent tests validate timestamps, and we may just have skipped a tick
+test_have_prereq !UTF8_ONLY_ENV ||
+test_tick
+
 test_expect_success 'import/export-marks' '
 
 	git checkout -b marks master &&