Move comment about python2 closer to the place it's used

Author: jyn514

src/ci/docker/host-x86_64/mingw-check-tidy/Dockerfile

@@ -1,8 +1,6 @@
 FROM ubuntu:22.04
 
 ARG DEBIAN_FRONTEND=noninteractive
-# NOTE: intentionally uses python2 for x.py so we can test it still works.
-# validate-toolstate only runs in our CI, so it's ok for it to only support python3.
 RUN apt-get update && apt-get install -y --no-install-recommends \
   g++ \
   make \
@@ -33,4 +31,6 @@ RUN pip3 install --no-deps --no-cache-dir --require-hashes -r /tmp/reuse-require
 COPY host-x86_64/mingw-check/validate-toolstate.sh /scripts/
 COPY host-x86_64/mingw-check/validate-error-codes.sh /scripts/
 
+# NOTE: intentionally uses python2 for x.py so we can test it still works.
+# validate-toolstate only runs in our CI, so it's ok for it to only support python3.
 ENV SCRIPT python2.7 ../x.py test --stage 0 src/tools/tidy tidyselftest