Fix UnsupportedOperationException when modifying an existing metadata.tools list

[mr-zepol]

This PR fixes the issue #571

[codacy-production]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
✅ +74.67%	✅ 84.21%

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (66fcb64)	0	0	0.00%
Head commit (51dc9d2)	6426 (+6426)	4798 (+4798)	74.67% (+74.67%)

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#574)	38	32	84.21%

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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[nscuro]

@mr-zepol Unfortunately there's now a merge conflict here. Happy to merge once that is resolved!

[mr-zepol]

@mr-zepol Unfortunately there's now a merge conflict here. Happy to merge once that is resolved!

Done

[nscuro]

Thanks @mr-zepol!