fix: pin Go version to 1.23 (minimum for MCP SDK compatibility)

The MCP Go SDK (modelcontextprotocol/go-sdk) requires Go 1.23+. Previous
commit accidentally bumped to 1.25 via go mod tidy on a newer toolchain.
Pin to 1.23 as the minimum compatible version — closest to our original
1.22 baseline. CI updated to match.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -19,7 +19,7 @@ jobs:
       - name: Set up Go
         uses: actions/setup-go@v5
         with:
-          go-version: '1.25'
+          go-version: '1.23'
 
       - name: Go Build
         run: |

go.mod

@@ -1,6 +1,6 @@
 module github.com/shankar0123/certctl
 
-go 1.25.0
+go 1.23.0
 
 require (
 	github.com/google/uuid v1.6.0