Ignore but report invalid keys

[SimplyDanny]

In other words, don't fall back to the default configuration due to invalid keys.

Fixes #5565.

[SwiftLintBot]

	17 Messages
📖	Linting Aerial with this PR took 0.8s vs 0.81s on main (1% faster)
📖	Linting Alamofire with this PR took 1.14s vs 1.17s on main (2% faster)
📖	Linting Brave with this PR took 6.52s vs 6.68s on main (2% faster)
📖	Linting DuckDuckGo with this PR took 3.44s vs 3.49s on main (1% faster)
📖	Linting Firefox with this PR took 9.23s vs 9.37s on main (1% faster)
📖	Linting Kickstarter with this PR took 8.11s vs 8.1s on main (0% slower)
📖	Linting Moya with this PR took 0.49s vs 0.49s on main (0% slower)
📖	Linting NetNewsWire with this PR took 2.41s vs 2.36s on main (2% slower)
📖	Linting Nimble with this PR took 0.69s vs 0.69s on main (0% slower)
📖	Linting PocketCasts with this PR took 6.84s vs 6.86s on main (0% faster)
📖	Linting Quick with this PR took 0.34s vs 0.34s on main (0% slower)
📖	Linting Realm with this PR took 4.02s vs 3.97s on main (1% slower)
📖	Linting Sourcery with this PR took 2.1s vs 2.12s on main (0% faster)
📖	Linting Swift with this PR took 3.91s vs 3.96s on main (1% faster)
📖	Linting VLC with this PR took 1.09s vs 1.14s on main (4% faster)
📖	Linting Wire with this PR took 14.25s vs 14.28s on main (0% faster)
📖	Linting WordPress with this PR took 9.78s vs 9.75s on main (0% slower)

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