build(deps): bump sigma_fun from `7f1ae3d` to `da6ffd2`

Bumps [sigma_fun](https://github.com/LLFourn/secp256kfun) from `7f1ae3d` to `da6ffd2`.
- [Release notes](https://github.com/LLFourn/secp256kfun/releases)
- [Commits](7f1ae3db39...da6ffd2ef4)

---
updated-dependencies:
- dependency-name: sigma_fun
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Cargo.lock

@@ -958,12 +958,11 @@ checksum = "5caaa75cbd2b960ff1e5392d2cfb1f44717fffe12fc1f32b7b5d1267f99732a6"
 [[package]]
 name = "ecdsa_fun"
 version = "0.7.1"
-source = "git+https://github.com/LLFourn/secp256kfun#e041ac08117e30170ac418047ecb734652e6b62c"
+source = "git+https://github.com/LLFourn/secp256kfun#da6ffd2ef4d58c84d508428356c92d92d5f11ac4"
 dependencies = [
  "bincode",
  "rand_chacha 0.3.1",
  "secp256kfun",
- "serde",
  "sigma_fun",
 ]
 
@@ -3273,7 +3272,7 @@ dependencies = [
 [[package]]
 name = "secp256kfun"
 version = "0.7.1"
-source = "git+https://github.com/LLFourn/secp256kfun#e041ac08117e30170ac418047ecb734652e6b62c"
+source = "git+https://github.com/LLFourn/secp256kfun#da6ffd2ef4d58c84d508428356c92d92d5f11ac4"
 dependencies = [
  "digest 0.10.5",
  "rand_core 0.6.2",
@@ -3470,7 +3469,7 @@ dependencies = [
 [[package]]
 name = "sigma_fun"
 version = "0.4.1"
-source = "git+https://github.com/LLFourn/secp256kfun#e041ac08117e30170ac418047ecb734652e6b62c"
+source = "git+https://github.com/LLFourn/secp256kfun#da6ffd2ef4d58c84d508428356c92d92d5f11ac4"
 dependencies = [
  "curve25519-dalek-ng",
  "digest 0.10.5",