Masking doesn't work on big-endian (s390x, sparc64)

2.44.1-1 in Debian experimental, on s390x:

# Storing test result image at /home/smcv/librsvg/tests/output/masking-intro-01-f-out.png
# 14276 pixels differ (with maximum difference of 237) from reference image

# Storing test result image at /home/smcv/librsvg/tests/output/masking-intro-01-f-diff.png
not ok 95 /rsvg-test/reftests/svg1.1/masking-intro-01-f.svg
FAIL: rsvg-test 95 /rsvg-test/reftests/svg1.1/masking-intro-01-f.svg

Reference:

s390x output:

Diff:

sparc64 has the same failure (with the same pixel count and difference) in its autobuilder log, although I haven't repeated that build in an environment where I can retrieve the output images.