.github/workflows: Fix missing dependency to LIBCOMPILER_RT

Following the merge of [0], the use of complex numbers requires the
external microlibrary `compiler-rt`[1].  Without this inclusion, builds
that set `CONFIG_LIBMUSL_COMPLEX` will fail.

[0]: unikraft/lib-musl#64
[1]: https://github.com/unikraft/lib-compiler-rt

Signed-off-by: Alexander Jung <alex@unikraft.io>
Reviewed-by: Razvan Deaconescu <razvand@unikraft.io>
Approved-by: Razvan Deaconescu <razvand@unikraft.io>
Tested-by: Unikraft CI <monkey@unikraft.io>
GitHub-Closes: #1033

.github/workflows/integration.yaml

@@ -86,6 +86,8 @@ jobs:
               kconfig:
                 CONFIG_MUSL: "y"
                 CONFIG_LIBMUSL_COMPLEX: "y"
+            compiler-rt:
+              version: staging
           targets:
           - platform: ${{ matrix.plat }}
             architecture: ${{ matrix.arch }}