ci: Split job, avoid running conformance/coverage w/ all toolchains

There is not point in running conformance tests and coverage checks with
all three toolchain versions in use for the rest of the CI. Let's split
into different jobs.

Signed-off-by: Quentin Monnet <quentin@isovalent.com>

.github/workflows/test.yaml

@@ -14,12 +14,6 @@ jobs:
   build_and_test:
     name: Build and test package
     runs-on: ubuntu-latest
-    env:
-      # Exclude features not supported by rbpf yet.
-      # atomic operations - https://github.com/qmonnet/rbpf/issues/47
-      # mem-len - Tests assume r2 contains the length of the memory.
-      KNOWN_FAILURES: "(lock|mem-len)"
-      CONFORMANCE_IMAGE: "ghcr.io/alan-jowett/bpf_conformance@sha256:547765717557e0f222de71fbf26f4bd9621c0149911aa03296024b469dd4598b"
     strategy:
       fail-fast: false
       matrix:
@@ -58,6 +52,30 @@ jobs:
         run: |
           cargo +${{ matrix.toolchain }} clippy
 
+  conformance_and_coverage:
+    name: Check eBPF conformance and code coverage
+    runs-on: ubuntu-latest
+    env:
+      # Exclude features not supported by rbpf yet.
+      # atomic operations - https://github.com/qmonnet/rbpf/issues/47
+      # mem-len - Tests assume r2 contains the length of the memory.
+      KNOWN_FAILURES: "(lock|mem-len)"
+      CONFORMANCE_IMAGE: "ghcr.io/alan-jowett/bpf_conformance@sha256:547765717557e0f222de71fbf26f4bd9621c0149911aa03296024b469dd4598b"
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v3
+
+      - name: Install toolchain (${{ matrix.toolchain }})
+        uses: actions-rs/toolchain@v1
+        with:
+          toolchain: nightly
+          override: true
+
+      - name: Build plug-in
+        run: |
+          cargo build --release --example rbpf_plugin
+
       - name: Run BPF conformance tests - Interpreter
         run: |
           docker run -v ${{github.workspace}}:/rbpf --rm \