test(gsadmin): Fix flake in BalanceChangeAction tests

[scttcper]

Attempting to silence this flake. I think the form is rerendering in some cases and the reference is to elements that have been deleted or will be deleted. Instead, in the waitFor re-query for the form field so we have the latest element.

flake https://github.com/getsentry/sentry/actions/runs/19270824639/job/55098367515

[codecov]

❌ 1 Tests Failed:

Tests completed	Failed	Passed	Skipped
12531	1	12530	10

View the top 1 failed test(s) by shortest run time

BalanceChangeAction re-enables form after error

Stack Traces | 5.12s run time

Error: Unable to find role="spinbutton" and name "Credit Amount"

Ignored nodes: comments, script, style
...
    at waitForWrapper (.../sentry/node_modules/.pnpm/@[email protected]/node_modules/@.../dom/dist/wait-for.js:163:27)
    at Object.<anonymous> (.../gsAdmin/components/changeBalanceAction.spec.tsx:207:18)

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[scttcper]

lol okay