Fix tox -e docs for macOS (#1694)

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### Summary

`tox -e docs` now works on my M1.

### Details and comments

We now say to install `.[all]` in two places: before installing the package itself when just installing `deps`, and then again when installing the package itself. Tox uses the same venv for both times, so that essentially results in a no-op in the second stage. This is similar to Qiskit/qiskit#9758.

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-minversion = 2.1
+minversion = 3.15.0
 envlist = py36, py37, py38, py39, py310, lint, docs
 skipsdist = True
 
@@ -33,13 +33,18 @@ commands =
   asv run {posargs}
 
 [testenv:docs]
+# Editable mode breaks macOS: https://github.com/sphinx-doc/sphinx/issues/10943
+usedevelop = false
 envdir = .tox/docs
 passenv = DOCS_FROM_MASTER QISKIT_DOCS_BUILD_TUTORIALS QISKIT_ENABLE_ANALYTICS
 extras =
   all
 deps =
   -r requirements-dev.txt
   sphinx-intl
+  # On macOS Tox 3.28, setting `extras` resulted in the package not being installed at all.
+  # It does not hurt to also install the package in the `deps` stage.
+  .[all]
 commands =
   sphinx-build -b html {posargs} -d {toxinidir}/docs/.doctrees {toxinidir}/docs/ {toxinidir}/docs/_build/html