terraform: bump golang to 1.21

Author: r4f4

terraform/Makefile

@@ -22,10 +22,8 @@ all: go-build
 
 .PHONY: go-mod-tidy-vendor
 go-mod-tidy-vendor: $(GO_MOD_TIDY_TARGETS)
-# The -compat=1.18 is needed for the openstack provider. The provider uses golang.org/x/mod, which go 1.18 selects
-# as v0.3.0 but go 1.16 selects as v0.4.2.
 $(GO_MOD_TIDY_TARGETS): go-mod-tidy-vendor.%:
-	cd providers/$* && go mod tidy -compat=1.18 && go mod vendor
+	cd providers/$* && go mod tidy && go mod vendor
 
 .PHONY: go-build
 go-build: $(GO_BUILD_TARGETS) go-build-terraform