Invariant syntax in opam config report doesn't match the expected syntax by --invariant

[kit-ty-kate]

opam config report since #5480 returns the invariant for the current switch:

# invariant            ocaml-base-compiler >= 5.0 & ocaml-base-compiler < 5.1

However this syntax isn't accepted by other parts of opam dealing with invariants (e.g. --invariant)
It should be something like:

# invariant            "ocaml-base-compiler" >= "5.0" & "ocaml-base-compiler" < "5.1"

instead

[rjbou]

It is displayed in a human readable way, it is not purpose of opam config report to be given as input of other commands.

[kit-ty-kate]

I disagree. I think having something consistent is more human readable than having 3 different incompatible syntaxes.