Added --diff flag to black in linting script

This prints the unified diff of formatting changes on failure,
making it easier to manually fix issues when black versions
disagree.

Signed-off-by: Lars Erik Wik <lars.erik.wik@northern.tech>

Author: larsewi

ci/linting.sh

@@ -10,7 +10,7 @@ pyright .
 
 shopt -s globstar
 echo "Running black"
-black --check .
+black --check --diff .
 
 echo "Running pyflakes"
 pyflakes .