Makefile: add missing PATH set

When running go test with sudo, the PATH must be set externally with
env PATH=$(PATH)
Add this in the helpers test rule.

Makefile

@@ -185,7 +185,7 @@ helpers-test-static-run: libbpfgo-static
 	CC=$(CLANG) \
 		CGO_CFLAGS=$(CGO_CFLAGS_STATIC) \
 		CGO_LDFLAGS=$(CGO_LDFLAGS_STATIC) \
-		sudo -E $(GO) test -v $(HELPERS)/...
+		sudo -E env PATH=$(PATH) $(GO) test -v $(HELPERS)/...
 
 helpers-test-dynamic-run: libbpfgo-dynamic
 	sudo $(GO) test -v $(HELPERS)/...