Speculative fix in relation tocoder/coder#14726

There have been several issues fixed in the plugin-sdk and its dependencies about go routines and the RPC protocol. Since ourcoder plugin is itself very, very simple in design (it generally just reads data from environment variables for data sources, and just does validation on resources), it's hard to imagine a hang in our provider schema code (not impossible tho). The error reports we've seen all show the Coder provider as the one that is involved intext file busy, so it seems likely that it's something unique about thecoder/coder provider.

hashicorp/kubernetes is used by both customers who reported thetext file busy error, and it is on SDK version 2.29+ and we were back on 2.20 before this PR.