Fix docs.rs build issue
From https://docs.rs/crate/librsvg/2.57.0-beta.3/builds/894175, this doesn't seem to be the "packages referenced by system-deps are not installed" problem, but rather that it's actually trying to build the cairo crate?
# rustc version
rustc 1.74.0-nightly (58eefc33a 2023-08-24)
# docs.rs version
docsrs 0.6.0 (9d80e3c8 2023-08-09)
# build log
[INFO] running `Command { std: "docker" "create" "-v" "/home/cratesfyi/workspace/builds/librsvg-2.57.0-beta.3/target:/opt/rustwide/target:rw,Z" "-v" "/home/cratesfyi/workspace/builds/librsvg-2.57.0-beta.3/source:/opt/rustwide/workdir:ro,Z" "-v" "/home/cratesfyi/workspace/cargo-home:/opt/rustwide/cargo-home:ro,Z" "-v" "/home/cratesfyi/workspace/rustup-home:/opt/rustwide/rustup-home:ro,Z" "-e" "SOURCE_DIR=/opt/rustwide/workdir" "-e" "CARGO_TARGET_DIR=/opt/rustwide/target" "-e" "DOCS_RS=1" "-e" "CARGO_HOME=/opt/rustwide/cargo-home" "-e" "RUSTUP_HOME=/opt/rustwide/rustup-home" "-w" "/opt/rustwide/workdir" "-m" "3221225472" "--cpus" "3" "--user" "1001:1001" "--network" "none" "ghcr.io/rust-lang/crates-build-env/linux@sha256:84cb280c7acaf12c1f874411053406050a24f846e52f817d4d9e64bcbe5ce959" "/opt/rustwide/cargo-home/bin/cargo" "+nightly" "rustdoc" "--lib" "-Zrustdoc-map" "-Z" "unstable-options" "--config" "build.rustflags=[\"--cfg\", \"docsrs\"]" "-Zhost-config" "-Ztarget-applies-to-host" "--config" "host.rustflags=[\"--cfg\", \"docsrs\"]" "--config" "build.rustdocflags=[\"-Z\", \"unstable-options\", \"--emit=invocation-specific\", \"--resource-suffix\", \"-20230824-1.74.0-nightly-58eefc33a\", \"--static-root-path\", \"/-/rustdoc.static/\", \"--cap-lints\", \"warn\", \"--disable-per-crate-search\", \"--extern-html-root-takes-precedence\"]" "--offline" "-Zunstable-options" "--config=doc.extern-map.registries.crates-io=\"https://docs.rs/{pkg_name}/{version}/x86_64-unknown-linux-gnu\"" "-Zrustdoc-scrape-examples" "-j3" "--target" "x86_64-unknown-linux-gnu", kill_on_drop: false }`
[INFO] [stderr] WARNING: Your kernel does not support swap limit capabilities or the cgroup is not mounted. Memory limited without swap.
[INFO] [stdout] f8de98fc88c2437f9cfff815ca2d90563928dee1a48854551fd821dd6229e238
[INFO] running `Command { std: "docker" "start" "-a" "f8de98fc88c2437f9cfff815ca2d90563928dee1a48854551fd821dd6229e238", kill_on_drop: false }`
[INFO] [stderr] warning: Target filter specified, but no targets matched. This is a no-op
[INFO] [stderr] Checking cairo-rs v0.18.0
[INFO] [stderr] Checking float-cmp v0.9.0
[INFO] [stderr] Checking encoding_rs v0.8.33
[INFO] [stderr] Checking language-tags v0.3.2
[INFO] [stderr] error[E0425]: cannot find function `cairo_pdf_surface_set_custom_metadata` in crate `ffi`
[INFO] [stderr] --> /opt/rustwide/cargo-home/registry/src/index.crates.io-6f17d22bba15001f/cairo-rs-0.18.0/src/pdf.rs:96:18
[INFO] [stderr] |
[INFO] [stderr] 96 | ffi::cairo_pdf_surface_set_custom_metadata(
[INFO] [stderr] | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: a function with a similar name exists: `cairo_pdf_surface_set_metadata`
[INFO] [stderr] |
[INFO] [stderr] ::: /opt/rustwide/cargo-home/registry/src/index.crates.io-6f17d22bba15001f/cairo-sys-rs-0.18.0/src/lib.rs:1227:5
[INFO] [stderr] |
[INFO] [stderr] 1227 | / pub fn cairo_pdf_surface_set_metadata(
[INFO] [stderr] 1228 | | surface: *mut cairo_surface_t,
[INFO] [stderr] 1229 | | metadata: cairo_pdf_metadata_t,
[INFO] [stderr] 1230 | | utf8: *const c_char,
[INFO] [stderr] 1231 | | );
[INFO] [stderr] | |_____- similarly named function `cairo_pdf_surface_set_metadata` defined here
[INFO] [stderr]
[INFO] [stderr] Checking rctree v0.5.0
[INFO] [stderr] For more information about this error, try `rustc --explain E0425`.
[INFO] [stderr] error: could not compile `cairo-rs` (lib) due to previous error
[INFO] [stderr] warning: build failed, waiting for other jobs to finish...
[INFO] running `Command { std: "docker" "inspect" "f8de98fc88c2437f9cfff815ca2d90563928dee1a48854551fd821dd6229e238", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "rm" "-f" "f8de98fc88c2437f9cfff815ca2d90563928dee1a48854551fd821dd6229e238", kill_on_drop: false }`
[INFO] [stdout] f8de98fc88c2437f9cfff815ca2d90563928dee1a48854551fd821dd6229e238