Make oss-fuzz mandatory

It has been disabled since some fuzzers were coming from
cncf/cncf-fuzzing repository and keeping them up-to-date was difficult.

However, the external repository is no longer used from oss-fuzz since
https://github.com/google/oss-fuzz/pull/8360.

As like other unit/integration tests, we should maintain the fuzzers in
this repository and fix any failures.

Signed-off-by: Kazuyoshi Kato <katokazu@amazon.com>

.github/workflows/fuzz.yml

@@ -12,15 +12,12 @@ jobs:
       uses: google/oss-fuzz/infra/cifuzz/actions/build_fuzzers@master
       with:
         oss-fuzz-project-name: 'containerd'
-        dry-run: true
         language: go
-      continue-on-error: true
     - name: Run Fuzzers
       uses: google/oss-fuzz/infra/cifuzz/actions/run_fuzzers@master
       with:
         oss-fuzz-project-name: 'containerd'
         fuzz-seconds: 300
-        dry-run: true
         language: go
       continue-on-error: true
     - name: Upload Crash