Fix issues with 'make generate' (#819)

This fixes issues in `make generate` that led to some generated
code in here being incorrect (generated from incorrect version of
protoc-gen-go) yet it was not being caught in CI.

The issues was that plugins were not made available in PATH to
the steps in a separate generate.sh script. And then that script
was failing to return a non-zero exit code when some of the steps
therein failed.

Author: jhump

Makefile

@@ -82,7 +82,7 @@ generate: $(BIN)/buf $(BIN)/protoc-gen-go $(BIN)/protoc-gen-connect-go $(BIN)/li
 	cd internal/conformance && go mod tidy
 	rm -rf internal/gen
 	PATH="$(abspath $(BIN))" buf generate
-	( cd cmd/protoc-gen-connect-go; ./generate.sh )
+	( cd cmd/protoc-gen-connect-go; PATH="$(abspath $(BIN)):$$PATH" ./generate.sh )
 	license-header \
 		--license-type apache \
 		--copyright-holder "The Connect Authors" \

cmd/protoc-gen-connect-go/generate.sh

@@ -1,2 +1,2 @@
 #!/bin/bash
-find testdata -maxdepth 1 -type d \( ! -name testdata \) -exec bash -c "cd '{}' && buf generate" \;
+find testdata -maxdepth 1 -type d \( ! -name testdata \) | xargs -n 1 -I % bash -c "cd '%' && buf generate"