Set Build to empty object because GetBuildObject will fill but not initialize it

[SaschaSchwarze0]

Changes

This fixes the following panic we see in AfterEach hooks of the e2e tests that actually prevent us to identify the root cause.

[PANICKED] Test Panicked
  In [AfterEach] at: /opt/hostedtoolcache/go/1.22.8/x64/src/runtime/panic.go:261 @ 10/30/24 14:53:26.63

  runtime error: invalid memory address or nil pointer dereference

  Full Stack Trace
    github.com/shipwright-io/build/pkg/reconciler/buildrun/resources.GetBuildObject({0x2358398?, 0xc00076aaa0?}, {0x2368620?, 0xc00076d5f0?}, 0xedeb43f66?, 0x0?)
    	/home/runner/work/build/build/pkg/reconciler/buildrun/resources/build.go:39 +0x28b
    github.com/shipwright-io/build/test/e2e/v1beta1_test.retrieveBuildAndBuildRun(0xc000102b60, {0xc00005c1d7?, 0x0?}, {0xc000429e75, 0xb})
    	/home/runner/work/build/build/test/e2e/v1beta1/common_test.go:147 +0x105

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Release Notes

NONE

[qu1queee]

/lgtm

[HeavyWombat]

/approve

[openshift-ci]

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