weboob/capabilities/bank: export Currency too

It makes sense to have it in bank caps too.
7 jobs for master in 13 minutes and 40 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #28570
build:3

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  Test
passed #28573
load-modules:3

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passed #28571
pyflakes:3

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passed #28572
pyflakes-strict:3

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passed #28574
unittests:3

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43.0%
failed #28575
allowed to fail
unittests-modules:3

00:08:14

42.0%
 
  Deploy
passed #28576
doc:3

00:01:22

 
Name Stage Failure
failed
unittests-modules:3 Test
        </head>
<body>
<h1>Error: 400 Bad Request</h1>
<p>Sorry, the requested URL <tt>'https://ci.weboob.org/api/v1/modules'</tt>
caused an error:</p>
<pre>Invalid JSON payload.</pre>
</body>
</html>
ERROR: Job failed: exit code 1