Add requirements.txt protobuf<=3.20.1 (ultralytics#8017)

* Pin `protobuf==3.20.1`

* Update requirements.txt

* Update ci-testing.yml

.github/workflows/ci-testing.yml

@@ -33,7 +33,7 @@ jobs:
       - name: Install requirements
         run: |
           python -m pip install --upgrade pip
-          pip install -r requirements.txt protobuf==3.20.1 coremltools openvino-dev tensorflow-cpu --extra-index-url https://download.pytorch.org/whl/cpu
+          pip install -r requirements.txt coremltools openvino-dev tensorflow-cpu --extra-index-url https://download.pytorch.org/whl/cpu
           python --version
           pip --version
           pip list
@@ -78,7 +78,7 @@ jobs:
       - name: Install requirements
         run: |
           python -m pip install --upgrade pip
-          pip install -r requirements.txt protobuf==3.20.1 --extra-index-url https://download.pytorch.org/whl/cpu
+          pip install -r requirements.txt --extra-index-url https://download.pytorch.org/whl/cpu
           python --version
           pip --version
           pip list

requirements.txt

@@ -12,6 +12,7 @@ scipy>=1.4.1  # Google Colab version
 torch>=1.7.0
 torchvision>=0.8.1
 tqdm>=4.41.0
+protobuf<=3.20.1  # https://github.com/ultralytics/yolov5/issues/8012
 
 # Logging -------------------------------------
 tensorboard>=2.4.1