update Makefile and default target

Adds a `sha256sum-$(VSN).txt`. For easier CI.

.build.yml

@@ -14,7 +14,7 @@ tasks:
   - lint: |
       make -C undocker -O -j$(nproc) lint
   - binaries: |
-      make -C undocker -O -j$(nproc) sha256sum.txt
-      cat undocker/sha256sum.txt
+      make -C undocker -O -j$(nproc) all
+      cat undocker/sha256sum-*.txt
 artifacts:
   - undocker/coverage.html

Makefile

@@ -24,7 +24,7 @@ $(foreach goosarch,$(GOOSARCHS),\
 	$(eval $(call undockertarget,$(word 1,$(subst /, ,$(goosarch))),$(word 2,$(subst /, ,$(goosarch))))))
 
 .PHONY: all
-all: $(UNDOCKERS)
+all: $(UNDOCKERS) sha256sum-$(VSN).txt
 
 .PHONY: lint
 lint: