sagemathgh-41214: Docs: small improvement for install instructions
    
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Fixing a small typo in that cython was declared twice, and added ninja
to the list of packages to install (normally it's installed on the fly
by meson-python, but it's a bit more robust to include it in the list).

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URL: sagemath#41214
Reported by: Tobias Diez
Reviewer(s):

Author: Release Manager

src/doc/en/installation/source.rst

@@ -173,10 +173,10 @@ To compile and install Sage in editable install, then just use:
         meson-python \
         "cypari2 >=2.2.1" \
         "cython >=3.0, != 3.0.3, != 3.1.0" \
-        "cython >=3.0, != 3.0.3" \
         "gmpy2 >=2.1.5" \
         memory_allocator \
         "numpy >=1.25" \
+        "ninja >=1.8.2" \
         jinja2 \
         setuptools
     $ uv sync --frozen --inexact --no-build-isolation