Makefile: use go install for install-gen-deps

The `go get' command for installing a module without modifying the
go.mod/go.sum was deprecated for several versions, and is now removed in
go 1.18.

Since the project supports go 1.17 at minimum, the behaviour is
supported too, and we can change this in the Makefile so the build works
on Go 1.18 too.

Makefile

@@ -52,12 +52,7 @@ install-build-deps: ## Install dependencies for bin build
 	@go install github.com/mitchellh/gox@v1.0.1
 
 install-gen-deps: ## Install dependencies for code generation
-	# to avoid having to tidy our go deps, we `go get` our binaries from a temp
-	# dir. `go get` will change our deps and the following deps are not part of
-	# out code dependencies; so a go mod tidy will remove them again. `go
-	# install` seems to install the last tagged version and we want to install
-	# master.
-	@(cd $(TEMPDIR) && GO111MODULE=on go get github.com/alvaroloes/enumer@master)
+	@GO111MODULE=on go install github.com/alvaroloes/enumer@master
 	@go install github.com/hashicorp/packer-plugin-sdk/cmd/packer-sdc@latest
 
 install-lint-deps: ## Install linter dependencies
@@ -203,4 +198,4 @@ help:
 
 # This is used for release builds by .github/workflows/build.yml
 version:
-	@$(CURDIR)/scripts/version.sh version/version.go
+	@$(CURDIR)/scripts/version.sh version/version.go