build(deps): bump third_party/icestorm from d20a5e9 to 1a40ae7 (#…

…3503)

Bumps [third_party/icestorm](https://github.com/YosysHQ/icestorm) from `d20a5e9` to `1a40ae7`.
- [Commits](YosysHQ/icestorm@d20a5e9...1a40ae7)

---
updated-dependencies:
- dependency-name: third_party/icestorm
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>