plugin: use API version for loading plugins

While migrating to a unified approach for loading plugins, the API
major and minor versions were not added to the constraints for
discovering plugins from the environment, leading to Packer potentially
considering plugins that are not compatible with itself.

This should not be possible, but was due to this omission, which we fix
with this commit.

packer/plugin.go

@@ -77,8 +77,10 @@ func (c *PluginConfig) Discover() error {
 	installations, err := plugingetter.Requirement{}.ListInstallations(plugingetter.ListInstallationsOptions{
 		PluginDirectory: c.PluginDirectory,
 		BinaryInstallationOptions: plugingetter.BinaryInstallationOptions{
-			OS:   runtime.GOOS,
-			ARCH: runtime.GOARCH,
+			OS:              runtime.GOOS,
+			ARCH:            runtime.GOARCH,
+			APIVersionMajor: pluginsdk.APIVersionMajor,
+			APIVersionMinor: pluginsdk.APIVersionMinor,
 			Checksummers: []plugingetter.Checksummer{
 				{Type: "sha256", Hash: sha256.New()},
 			},