fuzz: Add cifuzz integration

Add cifuzz workflow action to have fuzzers build and run on each
PR. This is a service offered by oss-fuzz where askama already runs.
cifuzz can help catch shallow bugs, regressions and fuzzing build
issues before they are merged into the repository, to do this
fuzzing will be run for ~3min.

.github/workflows/cifuzz.yml

@@ -0,0 +1,24 @@
+name: CIFuzz
+on: [pull_request]
+jobs:
+ Fuzzing:
+   runs-on: ubuntu-latest
+   steps:
+   - name: Build Fuzzers
+     id: build
+     uses: google/oss-fuzz/infra/cifuzz/actions/build_fuzzers@master
+     with:
+       oss-fuzz-project-name: 'askama'
+       language: rust
+   - name: Run Fuzzers
+     uses: google/oss-fuzz/infra/cifuzz/actions/run_fuzzers@master
+     with:
+       oss-fuzz-project-name: 'askama'
+       language: rust
+       fuzz-seconds: 180
+   - name: Upload Crash
+     uses: actions/upload-artifact@v3
+     if: failure() && steps.build.outcome == 'success'
+     with:
+       name: artifacts
+       path: ./out/artifacts