The `VirtualEnvironment` test helper is used in multiple places,but it is only told to install/upgrade `pip` when used from`test_installation`. It implements the functionality it wouldideally obtain by `upgrade_deps`, since the `upgrade_deps`parameter is only avaiilable in `venv` when using Python 3.9 andlater.When `pip` is installed, `upgrade_deps` would install `setuptools`when using Python 3.11 or lower, but not when using Python 3.12 orhigher. `VirtualEnvironment` does the same. (The reason for this isnot just to avoid needlessly departing from what `upgrade_deps`would do. Rather, it should not generally be necessary to have`setuptools` installed for package management since Python 3.12,and if it were necessary then this would a bug we would want todetect while running tests.)Previously this conditional specification of `setuptools` was doneby building different lists of package arguments to pass to `pip`,by checking `sys.version_info` to decide whether to append thestring `setuptools`.This commit changes how it is done, to use a static list of packagearguments instead. (The Python intepreter path continues to beobtained dynamically, but all its positional arguments, includingthose specifying packages, are now string literals.) Theconditional `setuptools` requirement is now expressed staticallyusing notation recognized by `pip`, as the string`setuptools; python_version<"3.12"`.

`setuptools` may potentially be needed for installation to workfully as desired prior to Python 3.12, so in those versions it isinstalled automatically in any virtual environment that is createdwith `pip` available. This is a behavior of the `venv` module thatis not specific to CI.However, on CI we upgrade packages that are preinstalled in thevirtual environment, or that we may otherwise wish to be present.This took the form of unconditionally installing/upgrading the`pip` and `wheel` packages, but conditionally upgrading the`setuptools` package only if we find that it is already installed.This commit changes the behavior to statically specify the samelist of package specifications to `pip` in all environments and inall versions of Python, but to use the static notation recognizedby `pip` to indicate that `setuptools` is to be instaled/upgradedonly if the Python version is strictly less than Python 3.12.This seems to be more readable. It also avoids using unquoted shellparameter expansion in a way that is potentially confusing (forexample, if we were running our CI script steps through ShellCheck,then it would automatically balk at that construction). It is alsomore consistent with how `test_installation` sets up itsenvironment (especially since31e1c03, but actually even beforethat, because it was still conditioning `setuptools` on the Pythonversion rather than whether it was already installed). Finally,this behavior is what the preexisting comment already described.This also adjusts the shell quoting style slightly in other relatedcommands (in the same workflows) that pass package specificationsto `pip`, for consistency.(For now, `".[test]"` rather than `.[test]` remains written in thereadme because it works in `cmd.exe` as well as other shells, butit may be changed there in the future too.)