ci: check for lack of byte-compilation warnings

As part of that we test with latest released Emacs version rather than
snapshot, because we don't want CI to start suddenly failing on
unrelated changes because upstream introduced a new warning/check.

.github/workflows/test.yml

@@ -12,7 +12,7 @@ jobs:
           - 25.3
           - 26.3
           - 27.1
-          - snapshot
+          - 29.2
     steps:
     - uses: purcell/setup-emacs@master
       with:

Makefile

@@ -30,7 +30,8 @@ compile: $(ELCFILES)
 OLDER_EMACS_DEFUNS = "(progn (defun undo-redo ())) (defun minibuffer-history-value()) (defun switch-to-minibuffer())"
 
 $(ELCFILES): %.elc: %.el
-	$(EMACS) --batch -Q -L . --eval $(OLDER_EMACS_DEFUNS) -f batch-byte-compile $<
+	$(EMACS) --batch -Q -L . --eval $(OLDER_EMACS_DEFUNS) \
+		--eval "(setq byte-compile-error-on-warn t)" -f batch-byte-compile $<
 
 # Byte-compile all files in one batch. This is faster than
 # compiling each file in isolation, but also less stringent.
@@ -59,7 +60,7 @@ clean:
 # The TAG variable may specify a test tag or a test name:
 #       make test TAG=repeat
 # This will only run tests pertaining to the repeat system.
-test:
+test: compile
 	$(EMACS) -nw -Q --batch -L . -l evil-tests.el \
 		--eval "(evil-tests-initialize '(${TAG}) '(${PROFILER}))"