ci: add v5.8.4-stable to PR-time matrix (supported back-compat line)

- _discover-versions.yml: extends wolfssl_latest_ref_array, so Simple,
  Cmdline, Sanitizers and SEED-SRC pick it up automatically.
- smoke-test.yml: third smoke build (5.8.4 + openssl-latest).
- multi-compiler.yml: gcc-12 + v5.8.4-stable + master openssl, alongside
  the existing v5.8.0-stable entry.

Author: aidangarske

.github/workflows/_discover-versions.yml

@@ -137,7 +137,8 @@ jobs:
             echo "wolfssl_ref=$WOLFSSL_DEB_REF"
             echo "wolfssl_ref_array=[\"master\",\"$WOLFSSL_DEB_REF\"]"
             echo "wolfssl_latest_ref=$WOLFSSL_LATEST"
-            echo "wolfssl_latest_ref_array=[\"master\",\"$WOLFSSL_LATEST\"]"
+            # v5.8.4-stable: supported back-compat line, always in PR matrix.
+            echo "wolfssl_latest_ref_array=[\"master\",\"$WOLFSSL_LATEST\",\"v5.8.4-stable\"]"
             echo "openssl_ref=openssl-$OSSL"
             echo "openssl_ref_array=[\"openssl-$OSSL\"]"
             echo "openssl_latest_ref=$OSSL_LATEST"

.github/workflows/multi-compiler.yml

@@ -55,6 +55,10 @@ jobs:
             CXX: g++-12
             wolfssl_ref: v5.8.0-stable
             openssl_ref: master
+          - CC: gcc-12
+            CXX: g++-12
+            wolfssl_ref: v5.8.4-stable
+            openssl_ref: master
           - CC: clang-13
             CXX: clang++-13
             wolfssl_ref: master

.github/workflows/smoke-test.yml

@@ -48,6 +48,8 @@ jobs:
             wolfssl_ref: master
           - name: stable/openssl-latest
             wolfssl_ref: ''  # filled in from needs.discover_versions
+          - name: 5.8.4/openssl-latest
+            wolfssl_ref: v5.8.4-stable
 
     steps:
       - name: Checkout wolfProvider