[Bug] Backports attempt to build Cryostat on the wrong branch

[ebaron]

The CI will try to build main regardless, which may fail due to API incompatibilities. Maybe using the pull request target branch would work?

cryostat-core/.github/workflows/ci.yml

Lines 79 to 84 in 159ee3b

	- uses: actions/checkout@v4
	with:
	repository: ${{ github.repository_owner }}/cryostat
	ref: main
	submodules: true
	fetch-depth: 0