Fix a bug when checking that the weights of the restriction matrix are equal to 1

[Rombur]

The bug was not in the way we compute the weights but in the way we check that the weights are one. The error was not picked up by the current tests because it requires agglomerates to have different sizes. Adding that kind of test is in the todo list see #37

Fix #67

[codecov-io]

Codecov Report

Merging #69 into master will increase coverage by 0.46%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #69      +/-   ##
==========================================
+ Coverage   88.09%   88.56%   +0.46%     
==========================================
  Files          22       20       -2     
  Lines        1235     1119     -116     
==========================================
- Hits         1088      991      -97     
+ Misses        147      128      -19

Impacted Files	Coverage Δ
include/mfmg/amge.templates.hpp	80.39% <100%> (+0.39%)	⬆️
include/mfmg/exceptions.hpp	15.38% <0%> (-15.39%)	⬇️
include/mfmg/dealii_operator.templates.hpp	57.3% <0%> (-12.93%)	⬇️
tests/test_hierarchy.cc	82.23% <0%> (-1.4%)	⬇️
include/mfmg/dealii_adapters.hpp	100% <0%> (ø)	⬆️
include/mfmg/concepts.hpp	100% <0%> (ø)	⬆️
tests/test_utils.cc
source/utils.cc
include/mfmg/hierarchy.hpp	97.64% <0%> (+2.24%)	⬆️
include/mfmg/dealii_operator.hpp	55.55% <0%> (+3.55%)	⬆️

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