Fix Valgrind error in the test suite

[fktn-k]

This PR has fixed errors reported by Valgrind.
The errors were due to missing std::fclose() calls after opening a test data file in the input_adapter class test cases.
So no changes have been made to the library source codes.

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Pull Request Checklist

Read the CONTRIBUTING.md file for detailed information.

• [x] Changes are described in the pull request or in a referenced issue.
• [x] The test suite compiles and runs without any error.
• [x] The code coverage on your branch is 100%.
• [x] The documentation is updated if you added/changed a feature.

Please don't

• The C++11 support varies between different compilers and versions. Please note the list of supported compilers. Some compilers like GCC 4.7 (and earlier), Clang 3.3 (and earlier), or Microsoft Visual Studio 13.0 and earlier are known not to work due to missing or incomplete C++11 support. Please refrain from proposing changes that work around these compiler's limitations with #ifdefs or other means.
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[github-actions[bot]]

:octocat: Upload Coverage Event Notification

Coverage data has been uploaded for the commit 7988d1c8dc28cd098d4e46ccd9fd8032a83b9a5d. You can download the artifact which contains the same file uploaded to the Coveralls and its HTML version.

Name	fkYAML_coverage.pr307.zip
ID	1398333619
URL	https://github.com/fktn-k/fkYAML/actions/runs/8618357114/artifacts/1398333619

[coveralls]

Pull Request Test Coverage Report for Build 8618357114

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 8602833627:	0.0%
Covered Lines:	3464
Relevant Lines:	3464

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💛 - Coveralls