fix(sdk): lock axum to 0.7.4

[mattstam]

Twirp requires axum 0.7.4

error: failed to select a version for `axum`.
    ... required by package `twirp v0.3.0 (https://github.com/github/twirp-rs.git?rev=c85f31f9c54957374e7dcb3534fc52cff0aa2dc5#c85f31f9)`
    ... which satisfies git dependency `twirp` of package `sp1-sdk v0.1.0 (https://github.com/succinctlabs/sp1.git?tag=v1.0.4-testnet#2ce75c6e)`
    ... which satisfies git dependency `sp1-sdk` of package `zkdna-script v0.1.0 (/Users/zachobront/code/zkdna/script)`
versions that meet the requirements `^0.7` (locked to 0.7.4) are: 0.7.4

all possible versions conflict with previously selected packages.

  previously selected package `axum v0.7.5`
    ... which satisfies dependency `axum = "=0.7.5"` of package `sp1-sdk v0.1.0 (https://github.com/succinctlabs/sp1.git?tag=v1.0.4-testnet#2ce75c6e)`
    ... which satisfies git dependency `sp1-sdk` of package `zkdna-script v0.1.0 (/Users/zachobront/code/zkdna/script)`

[puma314]

Btw, should we make sure this type of stuff gets caught in CI?

[mattstam]

At least with the .github/dependabot.yml for now it won't try to update