tools: check-imports using utf-8

[cclauss]

This PR uses io.open(encoding="utf-8") to resolve a UnicodeDecodeError on Python 3 after the fix in #30218 has been applied.

This can be replicated by running docker build . using the following:

Dockerfile

FROM ubuntu:bionic

# Install tools
RUN apt-get update
RUN apt-get install -y build-essential python3 python3-pip ninja-build make g++ vim git sudo

# Expose ports used by net tests
ENV NODE_COMMON_PORT=12346
EXPOSE 12346
# debug port used by v8 debugger
EXPOSE 5858
# debug port used by v8 insepctor
EXPOSE 9229

# Set up user node-dev: the tests fail when run by the root
RUN adduser --disabled-password --gecos '' node-dev
RUN adduser node-dev sudo
RUN echo '%sudo ALL=(ALL) NOPASSWD:ALL' >> /etc/sudoers
USER node-dev
WORKDIR /home/node-dev
ENV HOME /home/node-dev

# Clone the code and build
RUN git clone --depth=1 https://github.com/nodejs/node.git
WORKDIR /home/node-dev/node
RUN python3 -m pip install setuptools
RUN python3 ./configure --ninja
ENV BUILD_WITH ninja
RUN make -j2 test

Checklist

• commit message follows commit guidelines

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/26292/

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/26299/

[joyeecheung]

Thanks!

(And makes me wonder whether it is useful to add an dockerfile to BUILDING.md since it's pretty easy to understand what's necessary to have a working dev environment from a glance)

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/26334/

[cclauss]

Landed in aa4e54e

@targos is this in time for inclusion in #30262 ?