Add lightning invoice fuzzing to CI

Author: valentinewallace

.github/workflows/build.yml

@@ -207,7 +207,9 @@ jobs:
       - name: Sanity check fuzz targets on Rust ${{ env.TOOLCHAIN }}
         run: cd fuzz && RUSTFLAGS="--cfg=fuzzing" cargo test --verbose --color always
       - name: Run fuzzers
-        run: cd fuzz && ./ci-fuzz.sh
+        run: cd fuzz && ./ci-fuzz.sh && cd ..
+      - name: Run lightning-invoice fuzzers
+        run: cd lightning-invoice/fuzz && RUSTFLAGS="--cfg=fuzzing" cargo test --verbose && ./ci-fuzz.sh
 
   linting:
     runs-on: ubuntu-latest