Adding --require-hashes to the pip install commands.

PiperOrigin-RevId: 747487574
Change-Id: Ibfb8dbba8926bce9a2ea70802459df30f66efb5d

Author: ludoch

kokoro/gcp_ubuntu/publish_javadoc.sh

@@ -25,9 +25,9 @@ setup_docuploader() {
  sudo apt-get install -y python3 python3-pip maven
  # install docuploader package with upgrade to get latest correct versions.
  echo "Trying to install gcp-docuploader."
- python3 -m pip install --upgrade pip --user
- python3 -m pip install gcp-docuploader --user
- python3 -m pip install --upgrade protobuf --user
+ python3 -m pip install --require-hashes --upgrade pip --user
+ python3 -m pip install --require-hashes gcp-docuploader --user
+ python3 -m pip install --require-hashes --upgrade protobuf --user
 }
 
 if [[ -z "${CREDENTIALS}" ]]; then