Bump fuzz MSRV to 1.80

honggfuzz builds appear to fail on 1.75 - 1.79, so we just pick an
MSRV of the first toolchain that actually works.

The cargo command for testing binaries has also changed, which is
reflected here.

Author: TheBlueMatt

.github/workflows/build.yml

@@ -254,7 +254,9 @@ jobs:
   fuzz:
     runs-on: self-hosted
     env:
-      TOOLCHAIN: 1.75
+      # For whatever reason, honggfuzz doesn't build on 1.75, and there's not a lot of
+      # reason to insist on 1.75 for fuzzing, so we just pick an MSRV of 1.80 for fuzz.
+      TOOLCHAIN: 1.80
     steps:
       - name: Checkout source code
         uses: actions/checkout@v4
@@ -264,7 +266,7 @@ jobs:
       - name: Sanity check fuzz targets on Rust ${{ env.TOOLCHAIN }}
         run: |
           cd fuzz
-          RUSTFLAGS="--cfg=fuzzing --cfg=secp256k1_fuzz --cfg=hashes_fuzz" cargo test --verbose --color always --lib --bins -j8
+          RUSTFLAGS="--cfg=fuzzing --cfg=secp256k1_fuzz --cfg=hashes_fuzz" cargo test --verbose --color always --lib --bin -j8
           cargo clean
       - name: Run fuzzers
         run: cd fuzz && ./ci-fuzz.sh && cd ..