Fix compiler warnings for -Wrange-loop-construct

[ma8ma]

Fedora 42に投入されるgcc15開発版でcompileすると出る警告を解消します。
man gccによると、-Wrange-loop-construct は -Wall で有効になると書いてありますが、gcc14だとこの警告は出ません。

gcc15開発版のレポート(抜粋)

../src/article/font.cpp:85:25: warning: loop variable ‘<structured bindings>’ creates a copy from type ‘const int [2]’ [-Wrange-loop-construct]
../test/gtest_dbtree_nodetreebase.cpp:37:15: warning: loop variable ‘<structured bindings>’ creates a copy from type ‘const char* const [2]’ [-Wrange-loop-construct]
../test/gtest_dbtree_nodetreebase.cpp:53:15: warning: loop variable ‘<structured bindings>’ creates a copy from type ‘const char* const [2]’ [-Wrange-loop-construct]
../test/gtest_dbtree_nodetreebase.cpp:69:15: warning: loop variable ‘<structured bindings>’ creates a copy from type ‘const char* const [2]’ [-Wrange-loop-construct]
../test/gtest_dbtree_nodetreebase.cpp:85:15: warning: loop variable ‘<structured bindings>’ creates a copy from type ‘const char* const [2]’ [-Wrange-loop-construct]
../test/gtest_dbtree_nodetreebase.cpp:101:15: warning: loop variable ‘<structured bindings>’ creates a copy from type ‘const char* const [2]’ [-Wrange-loop-construct]
../test/gtest_dbtree_nodetreebase.cpp:117:15: warning: loop variable ‘<structured bindings>’ creates a copy from type ‘const char* const [2]’ [-Wrange-loop-construct]
../test/gtest_dbtree_nodetreebase.cpp:133:15: warning: loop variable ‘<structured bindings>’ creates a copy from type ‘const char* const [2]’ [-Wrange-loop-construct]
../test/gtest_dbtree_nodetreebase.cpp:149:15: warning: loop variable ‘<structured bindings>’ creates a copy from type ‘const char* const [2]’ [-Wrange-loop-construct]

パッチ作成の際に @mtasaka さんの[修正][1]を参考にしました。
バグ報告とパッチのご提供いただきまして、ありがとうございました。

[1] #1503 (comment)

Closes #1503