fuzz: Add cifuzz

This PR adds [cifuzz](https://google.github.io/oss-fuzz/getting-started/continuous-integration/) action workflow which is a service provided by oss-fuzz where this project already runs, this helps in catching shallow bugs, regression or build breakage by running fuzzers on PR for ~5 minutes (excluding the build time) on 'release/**' branch.

Author: manunio

.github/workflows/cifuzz.yml

@@ -0,0 +1,26 @@
+name: CIFuzz
+on:
+  schedule:
+  - cron: '0 12 * * 1' # 12pm Monday
+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: 'python-multipart'
+       language: python
+   - name: Run Fuzzers
+     uses: google/oss-fuzz/infra/cifuzz/actions/run_fuzzers@master
+     with:
+       oss-fuzz-project-name: 'python-multipart'
+       language: python
+       fuzz-seconds: 300
+   - name: Upload Crash
+     uses: actions/upload-artifact@v3
+     if: failure() && steps.build.outcome == 'success'
+     with:
+       name: artifacts
+       path: ./out/artifacts

python_multipart/multipart.py

@@ -1241,7 +1241,7 @@ def data_callback(name: CallbackName, end_i: int, remaining: bool = False) -> No
             elif state == MultipartState.HEADER_VALUE_ALMOST_DONE:
                 # The last character should be a LF.  If not, it's an error.
                 if c != LF:
-                    msg = "Did not find LF character at end of header " "(found %r)" % (c,)
+                    msg = "Did not find LF character at end of header (found %r)" % (c,)
                     self.logger.warning(msg)
                     e = MultipartParseError(msg)
                     e.offset = i