Fix broken docker/Dockerfile

[soehms]

As mentioned in #37856 (comment) the Dockerfile is broken by #37856. This will be fixed in this PR.

More precisely we replace install_scripts by appending $SAGE_ROOT/local/bin to the bash path variable. This does not affect Sage but ensures easy access to gap, maxima, ... in a bash session (see #37856 (comment) ff).

📝 Checklist

• The title is concise and informative.
• The description explains in detail what this PR is about.
• I have linked a relevant issue or discussion.
• I have created tests covering the changes.
• I have updated the documentation and checked the documentation preview.

⌛ Dependencies

[github-actions]

Documentation preview for this PR (built with commit c1407f9; changes) is ready! 🎉
This preview will update shortly after each push to this PR.

[mkoeppe]

LGTM.

[soehms]

LGTM.

Thanks!

For the record: Tested in this run after merging with #37986.

[soehms]

It seems that this didn't work as expected see this run for beta7 and this one for beta8, explicitly in the first case:

#16 64.41 [sagemath_doc_html-none] [spkg-install] sage -advanced > en/reference/repl/options.txt
#16 64.41 [sagemath_doc_html-none] [spkg-install] Traceback (most recent call last):
#16 64.41 [sagemath_doc_html-none] [spkg-install]   File "<frozen runpy>", line 198, in _run_module_as_main
#16 64.41 [sagemath_doc_html-none] [spkg-install]   File "<frozen runpy>", line 88, in _run_code
#16 64.41 [sagemath_doc_html-none] [spkg-install]   File "/home/sage/sage/local/var/lib/sage/venv-python3.11.8/lib/python3.11/site-packages/sage_docbuild/__main__.py", line 66, in <module>
#16 64.41 [sagemath_doc_html-none] [spkg-install]     from sage.env import SAGE_DOC_SRC
#16 64.41 [sagemath_doc_html-none] [spkg-install] ModuleNotFoundError: No module named 'sage'
#16 64.41 [sagemath_doc_html-none] [spkg-install] Error: 'sage --docbuild --all-documents' failed
#16 64.41 [sagemath_doc_html-none] [spkg-install] make[5]: *** [Makefile:41: doc-inventory-reference] Error 1

In the run for beta4 the module still was found.

@mkoeppe, do you have any idea what is missing?