[FIX] Moving the checkArgumentType error to its caller

[Iximiel]

Description

This is the PR about the problem I saw in #1167 and #1166

I think that the intended use of the original change I am fixing was to change the warning into an error, since I saw that it generates SEGFAULTs in case of keeping it as
a warning.

But the plumed_merror in the Keywords scope lose the information of having the information of the "culprit action" (and I think that plumed_merror is deprecated in favour of plumed_error, right?). So I simply changed the ->warning into an ->error to have the name of the action that arises the problem

I think this is more a "dev-side" problem than a "user-input" one, but it is still better to state to the user what is the action that may cause the error, since it can be "workarounded" as I did in #1166

checkArgumentType is only used in a single instance, so I think the modification is safe:

>git grep -n checkArgumentType
src/core/ActionWithArguments.cpp:195:    if( !readact->keywords.checkArgumentType( arg[i]->getRank(), arg[i]->hasDerivatives() ) ) {
src/tools/Keywords.cpp:693:bool Keywords::checkArgumentType( const std::size_t& rank, const bool& hasderiv ) const {
src/tools/Keywords.h:191:  bool checkArgumentType( const std::size_t& rank, const bool& hasderiv ) const ;

Target release

I would like my code to appear in release I ma targetting master but maybe v2.10 may be better?

Type of contribution

• changes to code or doc authored by PLUMED developers, or additions of code in the core or within the default modules
• changes to a module not authored by you
• new module contribution or edit of a module authored by you

Copyright

• I agree to transfer the copyright of the code I have written to the PLUMED developers or to the author of the code I am modifying.

• the module I added or modified contains a COPYRIGHT file with the correct license information. Code should be released under an open source license. I also used the command cd src && ./header.sh mymodulename in order to make sure the headers of the module are correct.

Tests

• I added a new regtest or modified an existing regtest to validate my changes.
• I verified that all regtests are passed successfully on GitHub Actions.