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.

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