chore: bump srtool to rust 1.93.0 (port of #1497 to main)

[gilescope]

Overview

Ports #1497 (merged into release/node-1.0.0) onto main.

midnight-storage-core 1.2.0-rc.3 pulled in konst 0.4.3, which raised its MSRV
to Rust 1.89. The srtool image was pinned to paritytech/srtool:1.88.0-0.18.3,
so deterministic runtime WASM builds failed at the cargo dependency check before
producing any artifact. Bumping both srtool-build and srtool-info targets to
paritytech/srtool:1.93.0-0.18.4 restores the build.

The toolchain change shifts the deterministic build baseline — downstream
consumers verifying srtool digests should re-anchor against the new image.

🗹 TODO before merging

• Ready

📌 Submission Checklist

• All commits are signed off (`git commit -s`) for the DCO
• Changes are backward-compatible (or flagged if breaking)
• Pull request description explains why the change is needed
• Self-reviewed the diff
• I have included a change file, or skipped for this reason:
• If the changes introduce a new feature, I have bumped the node minor version
• Update documentation (if relevant)
• Updated AGENTS.md if build commands, architecture, or workflows changed
• No new todos introduced

🧪 Testing Evidence

Same diff as #1497, which has already passed CI on `release/node-1.0.0`.
Local sanity:

```
$ git diff main..HEAD -- Earthfile | diffstat
Earthfile | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
```

• Additional tests are provided (if possible)

🔱 Fork Strategy

• Node Runtime Update
• Node Client Update
• Other:
• N/A — CI/build-only change (deterministic runtime WASM image bump).

Links

Cherry-pick of #1497.