Update URL of gpg key to use for kubectl install

Google are now serving the key in ascii armored format instead of
the previous binary format and as a result has broken the E2E docker
image build. To avoid installing additional tools such as gpg,
switch to the backup k8s URL which was implemented in response to
previous issues with the Google-hosted key being unavailable.

packages/e2e/Dockerfile

@@ -10,7 +10,7 @@
 # limitations under the License.
 
 FROM cypress/browsers:node18.12.0-chrome107
-RUN curl -fsSLo /usr/share/keyrings/kubernetes-archive-keyring.gpg https://packages.cloud.google.com/apt/doc/apt-key.gpg &&\
+RUN curl -fsSLo /usr/share/keyrings/kubernetes-archive-keyring.gpg https://dl.k8s.io/apt/doc/apt-key.gpg &&\
     echo "deb [signed-by=/usr/share/keyrings/kubernetes-archive-keyring.gpg] https://apt.kubernetes.io/ kubernetes-xenial main" | tee /etc/apt/sources.list.d/kubernetes.list &&\
     apt-get update && apt-get install -y \
     kubectl \