make: don't execute tilde files on test target

My system (Ubuntu 16.04) creates a backup when opening a file with
`vim`. This backup is called `filename~`. Due to it being a copy of the
file before opening, it also is executable, which is why it is selected
for execution with the `make test` target.

This change makes the `TESTS` macro exclude files ending in `~`. This
way files ending in `~` are not executed with `make test`.

Since e.g. projects like NextCloud are excluding such files also from
their sync [[1]], I think this is fine.

[1]: https://github.com/nextcloud/desktop/blob/d7b881feb6c2dbee84d9c49bef0f494afe25b6b8/sync-exclude.lst#L3

Author: miri64

Makefile.include

@@ -570,7 +570,7 @@ reset:
 	$(RESET) $(RESET_FLAGS)
 
 .PHONY: test test/available
-TESTS ?= $(foreach file,$(wildcard $(APPDIR)/tests/*),\
+TESTS ?= $(foreach file,$(wildcard $(APPDIR)/tests/*[^~]),\
                         $(shell test -f $(file) -a -x $(file) && echo $(file)))
 test: $(TEST_DEPS)
 	$(Q) for t in $(TESTS); do \