test: move http2-misbehaving-flow-control-paused
At least as currently written, test-http2-misbehaving-flow-control-paused is sensitive to resource constraints and has been observed to be unreliable in CI. Move it to sequential so it is not competing with other tests for resources.
Checklist
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make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
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