[llvm] [Github][CI] Add `doc8` for clang-tidy documentation formatting (PR #168827)

[via llvm-commits]

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@@ -94,6 +94,10 @@ COPY --from=llvm-downloader /llvm-extract/LLVM-${LLVM_VERSION}-Linux-X64/bin/cla
 COPY clang-tools-extra/clang-tidy/tool/clang-tidy-diff.py ${LLVM_SYSROOT}/bin/clang-tidy-diff.py
 
 # Install dependencies for 'pr-code-lint.yml' job
+RUN apt-get update && \
+    DEBIAN_FRONTEND=noninteractive apt-get install -y python3-doc8 && \
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zeyi2 wrote:

I think `doc8` is a pretty light dependency:
```
Package: python3-doc8
Version: 0.10.1-3
Installed-Size: 95.2 kB
Download-Size: 17.0 kB
```

The full build process is still running on my computer. So it will take some time before I can give a more accurate analysis. However, given that the only change in the Docker image is the addition of the `doc8` package, I don't think it will have a large impact. WDYT?

https://github.com/llvm/llvm-project/pull/168827