weboob/capabilities/bank: export Currency too

It makes sense to have it in bank caps too.
7 jobs for porting in 13 minutes and 33 seconds (queued for 2 seconds)
latest
Status Job ID Name Coverage
  Build
passed #28563
build:3

00:01:07

 
  Test
passed #28566
load-modules:3

00:02:20

passed #28564
pyflakes:3

00:02:35

passed #28565
pyflakes-strict:3

00:02:28

passed #28567
unittests:3

00:02:05

failed #28568
allowed to fail
unittests-modules:3

00:08:55

 
  Deploy
passed #28569
doc:3

00:01:18

 
Name Stage Failure
failed
unittests-modules:3 Test
-----------------------------------------------------------------------
TOTAL 70826 41109 42%
----------------------------------------------------------------------
Ran 370 tests in 419.557s

FAILED (SKIP=113, errors=149, failures=33)
=== Total coverage ===
MODULES COVERAGE: 42%
ERROR: Job failed: exit code 1