Update upload-artifact to v4

[pgherveou]

No description provided.

[alvicsam]

It seems that actions/cache should be updated as well to v4.2.0 or v3.4.0

[pgherveou]

@alvicsam not too sure what's going on, feel fre to take over

[alvicsam]

Now there is a build error in polkadot-westend and similar errors in cumulus:

║ error: failed to run custom build command for `westend-runtime v7.0.0 (/build/polkadot/runtime/westend)`
  ║
  ║ Caused by:
  ║ process didn't exit successfully: `/build/polkadot/runtime/westend/target/srtool/release/build/westend-runtime-1ea47616b8b5992c/build-script-build` (exit status: 1)
  ║ --- stdout
  ║ Information that should be included in a bug report.
  ║ Executing build command: env -u CARGO_ENCODED_RUSTFLAGS -u RUSTC CARGO_MAKEFLAGS="-j --jobserver-fds=10,13 --jobserver-auth=10,13" CARGO_TARGET_DIR="/build/polkadot/runtime/westend/target/srtool/release/wbuild/westend-runtime/target" RUSTFLAGS="-C target-cpu=mvp -C link-arg=--export-table -C link-arg=--export=__heap_base -C link-arg=--import-memory --cfg substrate_runtime " SKIP_WASM_BUILD="" "/home/builder/rustup/toolchains/1.81.0-x86_64-unknown-linux-gnu/bin/cargo" "rustc" "--target=wasm32-unknown-unknown" "--manifest-path=/build/polkadot/runtime/westend/target/srtool/release/wbuild/westend-runtime/Cargo.toml" "--color=always" "--profile" "release"
  ║ Using rustc version: rustc 1.81.0 (eeb90cda1 2024-09-04)
  ║
  ║ Compacted wasm in 9.034011293s
  ║ Compressed blob in 282.818557ms
  ║ Failed to deserialize `/build/polkadot/runtime/westend/target/srtool/release/wbuild/westend-runtime/westend_runtime.wasm`: UnknownOpcode(195)
  ║
  ║ --- stderr

Not sure that I can help with them.

[pgherveou]

@alvicsam looks like I fixed it for Westend but fellowship builds still rely on 1.81 rustc
can we merge this other PR #90 looks like it might help fix this.
I tweaked the the rustc_version for fellowship but it complains about missing wasm toolchain now