get cmake 3.22 when building on ubuntu 20 (#539)

.github/actions/openziti-tunnel-build-action/ubuntu-20.04/Dockerfile

@@ -1,5 +1,9 @@
+ARG CMAKE_VERSION="3.22.3"
+
 FROM ubuntu:focal
 
+ARG CMAKE_VERSION
+
 LABEL org.opencontainers.image.authors="[email protected],[email protected]"
 
 ENV DEBIAN_FRONTEND=noninteractive
@@ -12,7 +16,6 @@ WORKDIR /root/
 RUN apt-get -y update \
     && apt-get -y install \
         build-essential \
-        cmake \
         curl \
         doxygen \
         git \
@@ -25,5 +28,9 @@ RUN apt-get -y update \
         libssl-dev \
     && rm -rf /var/lib/apt/lists/*
 
+RUN curl -L https://cmake.org/files/v${CMAKE_VERSION%.*}/cmake-${CMAKE_VERSION}-linux-x86_64.sh -o cmake.sh \
+    && (bash cmake.sh --skip-license --prefix=/usr/local) \
+    && rm cmake.sh
+
 COPY ./entrypoint.sh /root/
 ENTRYPOINT [ "/root/entrypoint.sh" ]