Skip ImageMagick test in MinGW

ImageMagick 7.1.2-17 fails or crashes in MinGW. Skip the ImageMagick
test to avoid test failures in test_cmd_icc_profile.sh and
test_cmd_transform.sh.

Fixes https://github.com/AOMediaCodec/libavif/issues/3111.

tests/test_cmd_icc_profile.sh

diff --git a/tests/test_cmd_icc_profile.sh b/tests/test_cmd_icc_profile.sh
index 534f0ad..dfaa06f 100755
--- a/tests/test_cmd_icc_profile.sh
+++ b/tests/test_cmd_icc_profile.sh
@@ -77,6 +77,18 @@
   fi
   "${IMAGEMAGICK}" --version
 
+  # Avoid ImageMagick 7.1.2-17 errors in MinGW. See
+  # https://github.com/AOMediaCodec/libavif/issues/3111.
+  if [[ -n "${MSYSTEM:-}" ]]
+  then
+    echo "Skipping ImageMagick test in MinGW"
+    touch "${ENCODED_FILE}"
+    touch "${DECODED_FILE}"
+    touch "${CORRECTED_FILE}"
+    popd
+    exit 0
+  fi
+
   "${AVIFENC}" -s 8 -l "${INPUT_COLOR_PNG}" -o "${ENCODED_FILE}"
   # Old version of ImageMagick may not support reading ICC from AVIF.
   # Decode to PNG using avifdec first.

tests/test_cmd_transform.sh

diff --git a/tests/test_cmd_transform.sh b/tests/test_cmd_transform.sh
index 75d72af..2ef2636 100755
--- a/tests/test_cmd_transform.sh
+++ b/tests/test_cmd_transform.sh
@@ -95,6 +95,15 @@
   fi
   "${IMAGEMAGICK}" --version
 
+  # Avoid ImageMagick 7.1.2-17 errors in MinGW. See
+  # https://github.com/AOMediaCodec/libavif/issues/3111.
+  if [[ -n "${MSYSTEM:-}" ]]
+  then
+      echo "Skipping ImageMagick test in MinGW"
+      popd
+      exit 0
+  fi
+
   JPEG_PSNR_THRESHOLD=48
 
   # Crop