Pin 'npx prettier' version

If you don't do this, you get cruft from various autofixers competing.
diff --git a/bin/run-formatters.sh b/bin/run-formatters.sh
index 30087e3..0f740ee 100755
--- a/bin/run-formatters.sh
+++ b/bin/run-formatters.sh
@@ -38,13 +38,13 @@
   cd webui
   if [ "$CHECK_MODE" = true ]; then
     echo "Checking webui formatting with Prettier"
-    if ! npx prettier --check .; then
+    if ! npx prettier@3.5.3 --check .; then
       echo "Webui files need formatting"
       exit 1
     fi
   else
     echo "Fixing webui formatting with Prettier"
-    npx prettier --write .
+    npx prettier@3.5.3 --write .
     echo "Webui formatting complete"
   fi
 else