refactor: use xgettext-go from makefile variable

Easier to hack when customising xgettext-go.

Makefile

@@ -1,4 +1,5 @@
 ABRA         := ./cmd/abra
+XGETTEXT     := ./bin/xgettext-go
 COMMIT       := $(shell git rev-list -1 HEAD)
 GOPATH       := $(shell go env GOPATH)
 GOVERSION    := 1.24
@@ -60,8 +61,8 @@ update-po:
 	done
 
 .PHONY: update-pot
-update-pot: ./bin/xgettext-go
-	@./bin/xgettext-go \
+update-pot: $(XGETTEXT)
+	@${XGETTEXT} \
 		-o pkg/i18n/locales/$(DOMAIN).pot \
 		--keyword=i18n.G \
 		--keyword-ctx=i18n.GC \
@@ -69,7 +70,7 @@ update-pot: ./bin/xgettext-go
 		--add-comments-tag="translators" \
 		$$(find . -name "*.go" -not -path "*vendor*" | sort)
 
-./bin/xgettext-go:
+${XGETTEXT}:
 	@mkdir -p ./bin && \
 	wget -O ./bin/xgettext-go https://git.coopcloud.tech/toolshed/xgettext-go/raw/branch/main/xgettext-go && \
 	chmod +x ./bin/xgettext-go