Move COPY from R image to after the Python COPY

The R image is currently more frequently updated than the python one. Moving
this statement lower in the Dockerfile means we're more likely to take
advantage of caching to get slightly faster build times in most cases.

Dockerfile

@@ -33,19 +33,19 @@ RUN --mount=type=cache,target=/var/cache/apt \
     usermod -aG sudo rstudio &&\
     echo '%sudo ALL=(ALL) NOPASSWD:ALL' >> /etc/sudoers
 
-# copy the renv directory into the local site library from the OpenSAFELY R action image
+# Copy the Python virtualenv from OpenSAFELY Python action image
 #
 # DL3022: hadolint can't access a network and doesn't behave
 # as expected when a reference is made to an external image.
 # hadolint ignore=DL3022
-COPY --chown=rstudio:rstudio --from=ghcr.io/opensafely-core/r:latest /renv/lib/R-4.0/x86_64-pc-linux-gnu/ /usr/local/lib/R/site-library
+COPY --chown=rstudio:rstudio --from=ghcr.io/opensafely-core/python:v2 /opt/venv /opt/venv
 
-# Copy the Python virtualenv from OpenSAFELY Python action image
+# copy the renv directory into the local site library from the OpenSAFELY R action image
 #
 # DL3022: hadolint can't access a network and doesn't behave
 # as expected when a reference is made to an external image.
 # hadolint ignore=DL3022
-COPY --chown=rstudio:rstudio --from=ghcr.io/opensafely-core/python:v2 /opt/venv /opt/venv
+COPY --chown=rstudio:rstudio --from=ghcr.io/opensafely-core/r:latest /renv/lib/R-4.0/x86_64-pc-linux-gnu/ /usr/local/lib/R/site-library
 
 # Required for installing opensafely cli
 ENV PATH="/home/rstudio/.local/bin:${PATH}"