test: Nudge toward QT_STYLE_OVERRIDE=fusion on macOS

[maflcko]

Fixes bitcoin/bitcoin#35771

Using the Fusion style works around QTBUG-49686.

Otherwise, there could be an invalid call under the QMacStyle.

Can be tested via:

QT_STYLE_OVERRIDE=macOS  build/bin/test_bitcoin-qt  # fails
QT_STYLE_OVERRIDE=fusion build/bin/test_bitcoin-qt  # passes

[DrahtBot]

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Reviews

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Type	Reviewers
ACK	hebasto

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[hebasto]

Concept ACK. My current WIP branch also uses style overriding.

[hebasto]

So far, this bug has only been reproduced when Qt plugins are linked statically. Unfortunately, this configuration is not covered by CI.

[hebasto]

Are you sure that QTBUG-49686 is a good reference? Asking because it doesn't mention styles at all.

[maflcko]

Yeah, the issue is specific in the title, but the general issue is that a bunch of the code assumes Cocoa, and then throws/aborts/crashes when that assumption is violated with the Minimal platform plugin.

[hebasto]

ACK fa0c833, tested on macOS Tahoe 26.5.2 (Intel).

[hebasto]

@fanquake

Mind checking whether this PR resolves bitcoin/bitcoin#35771 for you?

[maflcko]

CI failure looks unrelated:

199/354 Test #202: test_kernel .......................................................***Failed    0.12 sec
Test setup error: system_error produced by: exp: Out of memory

[hebasto]

So far, this bug has only been reproduced when Qt plugins are linked statically. Unfortunately, this configuration is not covered by CI.

Apparently, @willcl-ark is working in that: bitcoin/bitcoin#35774.

[fanquake]

Mind checking whether this PR resolves bitcoin/bitcoin#35771 for you?

The tests pass with this change.

[DrahtBot]

🚧 At least one of the CI tasks failed.
_{Task Alpine (musl): https://github.com/bitcoin-core/gui/actions/runs/29917983667/job/88916243995
LLM reason (✨ experimental): CI failed because the test_kernel CTest job crashed during setup due to an out-of-memory error.}

Hints

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  affected test.

• An intermittent issue.

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