Fix build-* scripts to only target runtime directories (#2314)

Author: lc525

hack/build-images.sh

@@ -39,6 +39,7 @@ _main() {
   _buildImage "" $_version-slim
 
   for _runtimePath in "$ROOT_FOLDER/runtimes/"*/; do
+    [ -d "$_runtimePath" ] || continue
     _buildRuntimeImage $_runtimePath $_version
   done
 }

hack/build-wheels.sh

@@ -44,6 +44,7 @@ _main() {
   _buildWheel . $_outputPath
 
   for _runtime in "$ROOT_FOLDER/runtimes/"*/; do
+    [ -d "$_runtime" ] || continue
     echo "---> Building MLServer runtime: '$_runtime'"
     _buildWheel $_runtime $_outputPath
   done