Fix Go version matrix and coverage calculation fragility [FRE-4695]

- Update matrix from 1.21.x/1.22.x to 1.23.x to match go.mod
- Replace grep -oP with portable awk for coverage parsing
- Update security-scan job to use 1.23.x

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

.github/workflows/ci.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        go-version: [1.21.x, 1.22.x]
+        go-version: [1.23.x]
 
     steps:
     - uses: actions/checkout@v4
@@ -42,7 +42,7 @@ jobs:
 
     - name: Calculate coverage
       run: |
-        TOTAL=$(go test -cover ./... 2>&1 | grep -oP '\d+\.\d+%$' | head -1 | tr -d '%')
+        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"
@@ -74,7 +74,7 @@ jobs:
     - name: Set up Go
       uses: actions/setup-go@v5
       with:
-        go-version: 1.21.x
+        go-version: 1.23.x
 
     - name: Run GoSec
       uses: securego/gosec@v2