[hack] github/workflows: use QEMU with device tree support

Coconut QEMU does not have device tree support yet, so CI will fail
without this change.

Temporarily switch to my fork.

Signed-off-by: Luigi Leonardi <leonardi@redhat.com>

Author: luigix25

.github/workflows/qemu.yml

@@ -10,8 +10,8 @@ env:
   CARGO_TERM_COLOR: always
   # IGVM C wrapper might require a different Rust version than SVSM
   RUST_VERSION_IGVM: 1.84.1
-  QEMU_REPO: https://github.com/coconut-svsm/qemu.git
-  QEMU_REF: svsm-igvm
+  QEMU_REPO: https://github.com/luigix25/qemu.git
+  QEMU_REF: dtc_rebase
   IGVM_REPO: https://github.com/microsoft/igvm.git
   IGVM_REF: igvm-v0.3.4