The Linux CI workflows were still pinned to ladybird-ci:2026.05.4, even
though the CI image had since been rebuilt as 2026.05.25 after the Rust
toolchain switched to nightly.
This left CI running in an older container where cargo was not installed
for the nightly toolchain selected by the checked-out tree, causing Rust
crate builds to fail during the fuzzer host-tools build.
Update the workflow image references to the current published CI image.
f985ed83d4