deps: update go-plugin to 1.4.9 (#16292)

Fixes #16288. An earlier version of `go-plugin` introduced a warning log if
`SecureConfig` is unset. For Nomad and other applications that have "internal"
`go-plugin` consumers where the application runs itself as a plugin, this causes
spurious warn-level logs. For Nomad in particular this means every task driver
and logmon invocation emits the log, which is our primary operation.

The change was reverted upstream, so this changeset picks up the reverted
version.

go.mod

@@ -61,7 +61,7 @@ require (
 	github.com/hashicorp/go-memdb v1.3.4
 	github.com/hashicorp/go-msgpack v1.1.5
 	github.com/hashicorp/go-multierror v1.1.1
-	github.com/hashicorp/go-plugin v1.4.8
+	github.com/hashicorp/go-plugin v1.4.9
 	github.com/hashicorp/go-secure-stdlib/listenerutil v0.1.4
 	github.com/hashicorp/go-secure-stdlib/strutil v0.1.2
 	github.com/hashicorp/go-set v0.1.9

go.sum

@@ -862,8 +862,8 @@ github.com/hashicorp/go-multierror v1.1.0/go.mod h1:spPvp8C1qA32ftKqdAHm4hHTbPw+
 github.com/hashicorp/go-multierror v1.1.1 h1:H5DkEtf6CXdFp0N0Em5UCwQpXMWke8IA0+lD48awMYo=
 github.com/hashicorp/go-multierror v1.1.1/go.mod h1:iw975J/qwKPdAO1clOe2L8331t/9/fmwbPZ6JB6eMoM=
 github.com/hashicorp/go-plugin v1.4.3/go.mod h1:5fGEH17QVwTTcR0zV7yhDPLLmFX9YSZ38b18Udy6vYQ=
-github.com/hashicorp/go-plugin v1.4.8 h1:CHGwpxYDOttQOY7HOWgETU9dyVjOXzniXDqJcYJE1zM=
-github.com/hashicorp/go-plugin v1.4.8/go.mod h1:viDMjcLJuDui6pXb8U4HVfb8AamCWhHGUjr2IrTF67s=
+github.com/hashicorp/go-plugin v1.4.9 h1:ESiK220/qE0aGxWdzKIvRH69iLiuN/PjoLTm69RoWtU=
+github.com/hashicorp/go-plugin v1.4.9/go.mod h1:viDMjcLJuDui6pXb8U4HVfb8AamCWhHGUjr2IrTF67s=
 github.com/hashicorp/go-retryablehttp v0.5.3/go.mod h1:9B5zBasrRhHXnJnui7y6sL7es7NDiJgTc6Er0maI1Xs=
 github.com/hashicorp/go-retryablehttp v0.6.6/go.mod h1:vAew36LZh98gCBJNLH42IQ1ER/9wtLZZ8meHqQvEYWY=
 github.com/hashicorp/go-retryablehttp v0.7.0 h1:eu1EI/mbirUgP5C8hVsTNaGZreBDlYiwC1FZWkvQPQ4=