Fix a compilation error when old version of libfmt is used

[YanzhaoW]

Print the value of std::error_code instead since the formatter of std::error_code may not be supported in old versions of libfmt.

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Checklist:

• [x] Rebased against dev branch
• [x] My name is in the resp. CONTRIBUTORS/AUTHORS file
• [x] Followed the pull request guidlines and the Git workflow
• [x] Followed the seven rules of great commit messages