Adjust coverage CI job to download kernel artifact concurrently

Adjust the coverage CI job to download the kernel artifact concurrently
with the compilation of tests. This job is on the critical path of CI,
so making it as fast as possible minimizes overall CI runtime.

Signed-off-by: Daniel Müller <deso@posteo.net>

Author: d-e-s-o

.github/workflows/test.yml

@@ -219,34 +219,40 @@ jobs:
         echo "export PYTHON=${PYTHON}" >> env.sh
         source env.sh
 
-        cargo test --no-run --workspace --all-targets --features=zstd,nightly,blazesym-dev/generate-large-test-files 2>&1 | tee /tmp/cargo-build.log
-        tests=$(IFS='' grep Executable /tmp/cargo-build.log |
-          awk '{print $NF}' |
-          sed 's@[()]@@g' |
-          sed 's@.*@\0 --include-ignored@'
-        )
         # Yes, there appears to be no way to just retrieve the
         # uploaded artifact. One can't use actions/download-artifact
         # and provide any of the outputs of actions/upload-artifact.
         # Neither does it seem possible to just download the thing
         # directly, because contents are unconditionally zipped. Good.
         # Lord.
-        curl --location \
+
+        # Download artifact in parallel with test compilation. The unzip
+        # will produce the kernel bzImage and vmlinux.
+        (curl --location \
           --fail-with-body \
           --header "Accept: application/vnd.github+json" \
           --header "Authorization: Bearer ${{ secrets.GITHUB_TOKEN }}"\
           --header "X-GitHub-Api-Version: 2022-11-28" \
           --output artifact.zip \
-          "${ARTIFACT_URL}"
-        # This unzip will produce the kernel bzImage and vmlinux.
-        unzip artifact.zip
-        # Put vmlinux file into a location amenable to auto-discovery.
-        sudo mv vmlinux /boot/vmlinux-6.11.0
+          "${ARTIFACT_URL}" && unzip artifact.zip) &
+        artifact_pid=$!
+
+        cargo test --no-run --workspace --all-targets --features=zstd,nightly,blazesym-dev/generate-large-test-files 2>&1 | tee /tmp/cargo-build.log
+        tests=$(IFS='' grep Executable /tmp/cargo-build.log |
+          awk '{print $NF}' |
+          sed 's@[()]@@g' |
+          sed 's@.*@\0 --include-ignored@'
+        )
+
+        wait $artifact_pid
 
         cat <<EOF > main.sh
         #!/bin/sh
-        set -e
+        set -e -u
         . ./env.sh
+        mount -t tmpfs tmpfs /boot
+        # Put vmlinux file into a location amenable to auto-discovery.
+        mv vmlinux /boot/vmlinux-6.11.0
         $tests
         cargo llvm-cov report --ignore-filename-regex=cli/src/ --lcov --output-path lcov.info
         EOF