Run vulnerability scan on latest release version (#150)

Previously the scan ran on the current state of the codebase. This fails
to identify vulnerabilities in dependencies for the latest release
version if those dependencies have already been updated in the
development codebase. The gating factor for whether a new release is
required should be whether the previous release contains
vulnerabilities.

This change runs the scheduled vulnerability scan on the latest release
tag. It also adds vulnerability scanning to pull request builds. This is
purely informational. A scan failure does not fail the pull request
build.

Signed-off-by: Mark S. Lewis <Mark.S.Lewis@outlook.com>

.github/workflows/pull_request.yml

@@ -14,6 +14,9 @@ jobs:
   build:
     uses: ./.github/workflows/build.yml
 
+  scan:
+    uses: ./.github/workflows/scan.yml
+
   pull-request:
     needs: build
     name: Pull request success

.github/workflows/scan.yml

@@ -0,0 +1,25 @@
+name: "Security vulnerability scan"
+
+on:
+  workflow_call:
+    inputs:
+      ref:
+        description: Branch, tag or SHA to scan.
+        type: string
+        required: false
+        default: ""
+
+jobs:
+  scan:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          ref: ${{ inputs.ref }}
+      - name: Set up Go
+        uses: actions/setup-go@v5
+        with:
+          go-version: stable
+          check-latest: true
+      - name: Scan
+        run: make scan

.github/workflows/vulnerability-scan.yml

@@ -6,14 +6,18 @@ on:
   workflow_dispatch:
 
 jobs:
-  scan:
+  latest-release-version:
+    name: Get latest release tag
     runs-on: ubuntu-latest
+    outputs:
+      tag_name: ${{ steps.tag-name.outputs.value }}
     steps:
-      - uses: actions/checkout@v4
-      - name: Set up Go
-        uses: actions/setup-go@v5
-        with:
-          go-version: stable
-          check-latest: true
-      - name: Scan
-        run: make scan
+      - id: tag-name
+        run: echo "value=$(curl --location --silent --fail "https://api.github.com/repos/${GITHUB_REPOSITORY}/releases/latest" | jq --raw-output '.tag_name')" >> "${GITHUB_OUTPUT}"
+
+  scan:
+    name: Scan ${{ needs.latest-release-version.outputs.tag_name }}
+    needs: latest-release-version
+    uses: ./.github/workflows/scan.yml
+    with:
+      ref: ${{ needs.latest-release-version.outputs.tag_name }}