Add quotes to virtualenv template

[kmaragon]

Changelog: BugFix: Add quotes to virtualenv scripts, so they don't crash in pure sh shells.
Docs: Omit

Close #6264 with required quotes

• Refer to the issue that supports this Pull Request.
• N/A If the issue has missing info, explain the purpose/use case/pain/need that covers this Pull Request.
• I've read the Contributing guide.
• N/A I've followed the PEP8 style guides for Python code.
• N/A I've opened another PR in the Conan docs repo to the develop branch, documenting this one.

^{Note: By default this PR will skip the slower tests and will use a limited set of python versions. Check here how to increase the testing level by writing some tags in the current PR body text.}

[claassistantio]

All committers have signed the CLA.

[jgsogo]

Hi, @kmaragon ! Thanks a lot for taking care of #6264. I'll ask you a couple of things before merging this PR:

• this PR should be merged into branch release/1.21.1, we want to fix it in the next minor, so please, change the target branch (do not include other changesets from branch develop)
• tests are failing due to an extra blank. That is something marked as a FIXME so it is ok to add the extra blank and ensure that tests pass.

On the other hand, I'll propose a PR to develop changing our tests to more vanilla sh trying to reproduce the error reported originally, once those tests are ready they should show the error and this same changeset should fix them (I'll cherry-pick your changeset). Note.- If you want to add those tests here too it would be perfect, of course.

(Let us know if you need any help with the changes requested)

Thanks a lot!