Update dependency protobuf to v3.18.3 [SECURITY]

Author: renovate[bot]

docs/requirements.txt

@@ -114,7 +114,7 @@ markupsafe==1.1.1; python_version >= "2.7" and python_full_version < "3.0.0" or
     --hash=sha256:22c178a091fc6630d0d045bdb5992d2dfe14e3259760e713c490da5323866c39 \
     --hash=sha256:b7d644ddb4dbd407d31ffb699f1d140bc35478da613b441c582aeb7c43838dd8 \
     --hash=sha256:29872e92839765e546828bb7754a68c418d927cd064fd4708fab9fe9c8bb116b
-protobuf==3.15.8 \
+protobuf==3.18.3 \
     --hash=sha256:fad4f971ec38d8df7f4b632c819bf9bbf4f57cfd7312cf526c69ce17ef32436a \
     --hash=sha256:f17b352d7ce33c81773cf81d536ca70849de6f73c96413f17309f4b43ae7040b \
     --hash=sha256:4a054b0b5900b7ea7014099e783fb8c4618e4209fffcd6050857517b3f156e18 \