Add XMLName back to TestSuite struct

[pwschuurman]

What type of PR is this?

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/kind api-change
/kind bug
/kind cleanup
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What this PR does / why we need it: Test runners that rely on parsing pdcsi_junit.xml are not working. This was changed in #1911 when the XMLName was removed for an output struct.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

NONE

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[pwschuurman]

/retest

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@pwschuurman: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-gcp-compute-persistent-disk-csi-driver-kubernetes-integration	f1ca641	link	true	/test pull-gcp-compute-persistent-disk-csi-driver-kubernetes-integration

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