Auto merge of #18364 - mantaroh:svgpaintkind-interpolation, r=birtles

Don't allow interpolating SVGPaintKind::None.

This is a PR for https://bugzilla.mozilla.org/show_bug.cgi?id=1396483

PR #18103 disallowed interpolation between fill:none and fill:none, but that change was regressed by the refactoring in PR #18239.
This patch restores the intended behavior, disabling animation of SVGPaintKind::None.

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There are already these tests in dom/smil/tests of gecko, this PR will enable these tests.
For detail, see https://bugzilla.mozilla.org/show_bug.cgi?id=1396483 .

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