Add spaces to opam root during CI

[jonahbeckford]

It is very common to have spaces in directory paths on Windows (ex. C:\Users\Jane Smith) and is not unusual on macOS either. Packages should not fail to build simply because a user has a space in their path.

The suggestion is to change the opam root to include a space. Examples:

• /home/runner/work/has space
• /home/has space
• D:/a/has space
• C:/GitLab-Runner/builds/has space

The suggestion is to make the default in a new version of CI (ex. setup-ocaml.v2.1.0) use a space since it is a bug to not support spaces. However, if the field x-validation-path-with-spaces: false is present in all .opam files (can use awk to check), then no space should be used.

Cross-links:

• Add spaces to opam root during CI ocaml/setup-ocaml#634
• Add spaces to opam root during setup-dkml CI diskuv/dkml-workflows#8
• OCaml Appveyor CI does something similar

[kit-ty-kate]

It turns out OCaml itself doesn't support directories with spaces on non-Windows platforms: ocaml/ocaml#11590

I could try and see if there is a hack we could do to work around this but this sounds ugly and quite tricky. Asking @Octachron for a backport and a release seems to be a more reasonable path towards fixing this.