fix(action): return correct error variable in prepareUpgrade

When Deployed() succeeds but releaserToV1Release() fails, prepareUpgrade
returned err (nil) instead of cerr (the conversion error), causing a
silent nil return that could lead to nil pointer dereferences downstream.

Closes #32007

Signed-off-by: Rhys McNeill <rhysmcneill7@hotmail.co.uk>

pkg/action/upgrade.go

@@ -253,7 +253,7 @@ func (u *Upgrade) prepareUpgrade(name string, chart *chartv2.Chart, vals map[str
 		var cerr error
 		currentRelease, cerr = releaserToV1Release(currentReleasei)
 		if cerr != nil {
-			return nil, nil, false, err
+			return nil, nil, false, cerr
 		}
 		if err != nil {
 			if errors.Is(err, driver.ErrNoDeployedReleases) &&