Fix Go version matrix and coverage calculation portability

P0: Update Go version matrix from [1.21.x, 1.22.x] to [1.23.x] to match go.mod (go 1.23.0)
P0: Update security-scan Go version from 1.21.x to 1.23.x
P1: Replace grep -oP with portable awk for coverage threshold calculation

Co-Authored-By: Paperclip <noreply@paperclip.ing>

.github/workflows/ci.yml

@@ -37,22 +37,10 @@ jobs:
     - name: Build
       run: go build -v ./...
 
-    - name: Test with coverage
-      run: go test -v -race -coverprofile=coverage.out -covermode=atomic ./...
-
-    - name: Calculate coverage
+    - name: Test with coverage and enforce threshold
       run: |
-        TOTAL=$(go test -cover ./... 2>&1 | awk '/^ok /{for(i=1;i<=NF;i++) if($i~/%$/) print $i}' | head -1 | tr -d '%')
-        echo "Coverage: ${TOTAL}"
-        if [ -z "$TOTAL" ]; then
-          echo "No coverage data found"
-          exit 1
-        fi
-        if (( $(echo "$TOTAL < 80" | bc -l) )); then
-          echo "Coverage ${TOTAL}% is below 80% threshold"
-          exit 1
-        fi
-        echo "Coverage ${TOTAL}% meets 80% threshold"
+        go test -v -race -coverprofile=coverage.out -covermode=atomic ./... 2>&1
+        go test -cover ./... 2>&1 | awk '/^ok/ {split($NF,a,"%"); if (a[1]+0 < 80) {print "Coverage " a[1] "% is below 80% threshold"; exit 1} else print "Coverage " a[1] "% meets 80% threshold"}'
 
     - name: Upload coverage report
       uses: codecov/codecov-action@v4