NiceMonomorphism regression

[fingolfin]

Unfortunately PR #5029 causes a regression in a bunch of packages, see this report:

• fr - fix in set IsInjective flag before calling SetNiceMonomorphism gap-packages/fr#55, available in version 2.4.11
• groupoids - fix in Mark nice monomorphisms explicitly as injective gap-packages/groupoids#51, not yet available in version 1.71
• rcwa - fix in set IsInjective flag for nice monomorphism ... gap-packages/rcwa#25, not yet available in version 4.7.0
• semigroups - fix in set IsInjective flag before calling SetNiceMonomorphism semigroups/Semigroups#870, not yet available in version 5.0.2
• xmod - probably inherits this from groupoids

I think we need to disable this error for now -- or perhaps turn it into an InfoWarning, but the warning must not be shown on the default level as that would still break those test suites).

On the long run, someone can submit PRs to each of those packages to fix them up, and once they all had a release, we can re-enable the error.

[ IMHO this also answers whether we should backport that PR ;-) ]

[ThomasBreuer]

I am not surprised about these problems, I was rather surprised that the problems with the previous code (infinite recursion when calling Kernel) were not observed earlier.

I am still convinced that #5029 is a reasonable bugfix. (And the "regression" label looks funny from this point of view.)
Replacing the error message by a warning that is not shown does not look sensible to me.

For the moment, I think that reverting the changes from #5029 is the only way to avoid the failures in the tests of the packages.
Adjusting these packages to the intended changes is technically not difficult. Let us see how this goes on.

[fingolfin]

All of these are resolved by now, so I guess we could re-enable the strict check for this

[ThomasBreuer]

The problem is fixed in the development versions of the packages in question, but not yet in released versions.
Currently the latest released versions of groupoids (1.71), rcwa (4.7.0), and Semigroups (5.0.2) do not contain the fix.

[fingolfin]

I believe all packages had updates with the fixes in them by now.