Clarify ESM migration details in README for V7

Author: priyagupta108

README.md

@@ -12,7 +12,7 @@ This action provides the following functionality for GitHub Actions users:
 - Registering problem matchers for error output
 ## Breaking changes in V7
 
-- **Migrated to ESM** to enable support for the latest `@actions/*` package versions.
+- Migrated action internals to ESM for compatibility with latest `@actions/*` packages. No changes to action inputs, outputs, or behavior.
 
 ## Breaking changes in V6
 

dist/setup/index.js

@@ -98317,7 +98317,13 @@ async function installPython(workingDirectory) {
                 info(data.toString().trim());
             },
             stderr: (data) => {
-                core_error(data.toString().trim());
+                const msg = data.toString().trim();
+                if (/^WARNING:/im.test(msg)) {
+                    warning(msg);
+                }
+                else {
+                    core_error(msg);
+                }
             }
         }
     };