ci: try to work around issues with the test cleanup

It seems that on some build agents, there might be some transient file
locking issues, so when we cannot delete the trash directory, let's be
gentle and try again five seconds later, and only error out if it still
fails the second time.

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

t/test-lib.sh

@@ -1011,7 +1011,11 @@ test_done () {
 			error "Tests passed but trash directory already removed before test cleanup; aborting"
 
 			cd "$TRASH_DIRECTORY/.." &&
-			rm -fr "$TRASH_DIRECTORY" ||
+			rm -fr "$TRASH_DIRECTORY" || {
+				# try again in a bit
+				sleep 5;
+				rm -fr "$TRASH_DIRECTORY"
+			} ||
 			error "Tests passed but test cleanup failed; aborting"
 		fi
 		test_at_end_hook_