feat: Fix minimum supported cargo version to 1.77

This should ensure, that our Cargo.lock file stays at version 3
when using `cargo update` or dependabot.

.github/workflows/qc.yaml

@@ -159,6 +159,7 @@ jobs:
 
   cargo-fuzz:
     runs-on: ubicloud-standard-2-ubuntu-2204
+    env:
     steps:
       - uses: actions/checkout@v4
       - uses: actions/cache@v4
@@ -173,7 +174,7 @@ jobs:
       - name: Install nightly toolchain
         run: |
           rustup toolchain install nightly
-          rustup default nightly
+          rustup override nightly
       - name: Install cargo-fuzz
         run: cargo install cargo-fuzz
       - name: Run fuzzing
@@ -209,4 +210,5 @@ jobs:
           files: ./target/grcov/lcov
           verbose: true
         env:
+          RUSTUP_TOOLCHAIN: 1.81
           CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}