test: retrofit tests for new validation

Accoring to new validation in ADD and COPY if there are multiple sources
then destination must specify that it is a directory

Signed-off-by: Aditya R <[email protected]>

Author: flouthoc

tests/bud/copy-globs/Containerfile

@@ -1,3 +1,3 @@
 FROM scratch
 # *txt exists so should succeed
-COPY *.txt /testdir
+COPY *.txt /testdir/