Address minor shell script linter warnings

.github/workflows/rename_project.sh

@@ -1,11 +1,13 @@
 #!/usr/bin/env bash
-while getopts a:n:u:d: flag
+# vim:sw=2:ts=2:sts=2:et
+while getopts a:n:u: flag
 do
-    case "${flag}" in
-        a) owner=${OPTARG};;
-        n) name=${OPTARG};;
-        u) url=${OPTARG};;
-    esac
+  case "${flag}" in
+    a) owner=${OPTARG};;
+    n) name=${OPTARG};;
+    u) url=${OPTARG};;
+    *) echo "Invalid flag: ${flag}"; exit 1;;
+  esac
 done
 
 echo "Owner: $owner";
@@ -19,10 +21,10 @@ original_name="{{REPOSITORY_NAME}}"
 original_url="{{REPOSITORY_URL}}"
 for filename in $(git ls-files)
 do
-    sed -i "s/$original_owner/$owner/g" $filename
-    sed -i "s/$original_name/$name/g" $filename
-    sed -i "s/$original_url/$url/g" $filename
-    echo "Renamed $filename"
+  sed -i "s/$original_owner/$owner/g" "$filename"
+  sed -i "s/$original_name/$name/g" "$filename"
+  sed -i "s/$original_url/$url/g" "$filename"
+  echo "Renamed $filename"
 done
 
 # This command runs only once on GHA!