Correct the checksum and download link

templates/tools/dockerfile/test/python_stretch_default_x64/Dockerfile.template

@@ -20,14 +20,15 @@
   RUN apt-get update && apt-get install -y jq build-essential libffi-dev
 
   RUN cd /tmp && ${'\\'}
-    wget -q https://github.com/python/cpython/archive/v3.6.9.tar.gz && ${'\\'}
-    tar xzvf v3.6.9.tar.gz && ${'\\'}
-    cd cpython-3.6.9 && ${'\\'}
+    wget -q https://www.python.org/ftp/python/3.6.9/Python-3.6.9.tgz && ${'\\'}
+    tar xzvf Python-3.6.9.tgz && ${'\\'}
+    cd Python-3.6.9 && ${'\\'}
     ./configure && ${'\\'}
     make install
   
-  RUN echo "ff7cdaef4846c89c1ec0d7b709bbd54d v3.6.9.tar.gz" > checksum.md5
-  RUN md5sum -c checksum.md5
+  RUN cd /tmp && ${'\\'}
+    echo "ff7cdaef4846c89c1ec0d7b709bbd54d Python-3.6.9.tgz" > checksum.md5 && ${'\\'}
+    md5sum -c checksum.md5
 
   RUN apt-get update && apt-get -t buster install -y python3.7 python3-all-dev
   RUN curl https://bootstrap.pypa.io/get-pip.py | python3.7

tools/dockerfile/test/python_stretch_default_x64/Dockerfile

@@ -69,14 +69,15 @@ RUN apt-get update && apt-get install -y zlib1g-dev libssl-dev
 RUN apt-get update && apt-get install -y jq build-essential libffi-dev
 
 RUN cd /tmp && \
-  wget -q https://github.com/python/cpython/archive/v3.6.9.tar.gz && \
-  tar xzvf v3.6.9.tar.gz && \
-  cd cpython-3.6.9 && \
+  wget -q https://www.python.org/ftp/python/3.6.9/Python-3.6.9.tgz && \
+  tar xzvf Python-3.6.9.tgz && \
+  cd Python-3.6.9 && \
   ./configure && \
   make install
 
-RUN echo "ff7cdaef4846c89c1ec0d7b709bbd54d v3.6.9.tar.gz" > checksum.md5
-RUN md5sum -c checksum.md5
+RUN cd /tmp && \
+  echo "ff7cdaef4846c89c1ec0d7b709bbd54d Python-3.6.9.tgz" > checksum.md5 && \
+  md5sum -c checksum.md5
 
 RUN apt-get update && apt-get -t buster install -y python3.7 python3-all-dev
 RUN curl https://bootstrap.pypa.io/get-pip.py | python3.7