test: do not build firecracker before running kani

Kani has no use for pre-built binaries, and I'm fairly certain it cannot
even reuse the build artifacts due to using a different toolchain. So
pass `--no-build` to `devtool test` when running the kani test to safe a
few more minutes there.

Signed-off-by: Patrick Roy <[email protected]>

Author: roypat

.buildkite/pipeline_pr.py

@@ -51,7 +51,7 @@
 ):
     kani_grp = pipeline.build_group(
         "🔍 Kani",
-        "./tools/devtool -y test -- ../tests/integration_tests/test_kani.py -n auto",
+        "./tools/devtool -y test --no-build -- ../tests/integration_tests/test_kani.py -n auto",
         # Kani step default
         # Kani runs fastest on m6a.metal
         instances=["m6a.metal"],