Silence dubious ownership issue in bazel image (#30963)

* Silence dubious ownership issue in bazel image

* Agh. It's a template

templates/tools/dockerfile/test/bazel/Dockerfile.template

@@ -18,6 +18,8 @@
   <%include file="../../bazel.include"/>
   
   RUN mkdir -p /var/local/jenkins
+
+  RUN git config --global --add safe.directory /var/local/jenkins/grpc
   
   # Define the default command.
   CMD ["bash"]

tools/dockerfile/test/bazel/Dockerfile

@@ -60,5 +60,7 @@ RUN BAZEL_ARCH_SUFFIX="$(uname -m | sed s/aarch64/arm64/)" \
 
 RUN mkdir -p /var/local/jenkins
 
+RUN git config --global --add safe.directory /var/local/jenkins/grpc
+
 # Define the default command.
 CMD ["bash"]