Do not create files in TESTDATA_DIR in sh tests (#2415)

diff --git a/tests/test_cmd_avifgainmaputil.sh b/tests/test_cmd_avifgainmaputil.sh
index 096aad5..c3f8965 100755
--- a/tests/test_cmd_avifgainmaputil.sh
+++ b/tests/test_cmd_avifgainmaputil.sh
@@ -34,15 +34,12 @@
 INPUT_AVIF_GAINMAP_HDR="${TESTDATA_DIR}/seine_hdr_gainmap_srgb.avif"
 INPUT_AVIF_GAINMAP_HDR2020="${TESTDATA_DIR}/seine_hdr_rec2020.avif"
 INPUT_JPEG_AVIF_GAINMAP_SDR="${TESTDATA_DIR}/seine_sdr_gainmap_srgb.jpg"
-AVIF_GAINMAP_SDR_WITH_ICC="${TESTDATA_DIR}/seine_sdr_gainmap_srgb_icc.jpg" # generated below
+AVIF_GAINMAP_SDR_WITH_ICC="seine_sdr_gainmap_srgb_icc.jpg" # generated below
 # Output file names.
 AVIF_OUTPUT="avif_test_cmd_avifgainmaputil_output.avif"
 JPEG_OUTPUT="avif_test_cmd_avifgainmaputil_output.jpg"
 PNG_OUTPUT="avif_test_cmd_avifgainmaputil_output.png"
 
-# generate another input file used in tests below
-"${AVIFENC}" "${INPUT_JPEG_AVIF_GAINMAP_SDR}" "${AVIF_GAINMAP_SDR_WITH_ICC}"  --qcolor 90 --qgain-map 90
-
 # Cleanup
 cleanup() {
   pushd ${TMP_DIR}
@@ -52,6 +49,9 @@
 trap cleanup EXIT
 
 pushd ${TMP_DIR}
+  # generate another input file used in tests below
+  "${AVIFENC}" "${INPUT_JPEG_AVIF_GAINMAP_SDR}" "${AVIF_GAINMAP_SDR_WITH_ICC}" --qcolor 90 --qgain-map 90
+
   "${AVIFGAINMAPUTIL}" help
 
   "${AVIFGAINMAPUTIL}" printmetadata "${INPUT_AVIF_GAINMAP_SDR}"