Fix the dependency of ark-sponge in Cargo.toml

[weikengchen]

Description

Since a PR in ark-sponge is merged and the corresponding branch is deleted, Cargo.toml is no longer able to find that branch. This PR fixes so.

Closes #82

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Before we can merge this PR, please make sure that all the following items have been checked off. If any of the checklist items are not applicable, please leave them but write a little note why.

• [x] Targeted PR against correct branch (main)
• [x] Linked to Github issue with discussion and accepted design OR have an explanation in the PR that describes this work.
• [ ] Wrote unit tests
• [ ] Updated relevant documentation in the code
• [ ] Added a relevant changelog entry to the Pending section in CHANGELOG.md
• [x] Re-reviewed Files changed in the Github PR explorer

[weikengchen]

The main purpose here is to see how many other things are broken based on the GitHub actions as we have changes in ark-algebra that may not have been sufficiently synchronized