Update test_de.py: "ein Mark" must be "eine Mark" instead

[m-f-h]

Update test_de.py: "ein Mark" must be "eine Mark" instead, cf. issue #462 and patch #471

Fixes #462 by @rillig

Changes proposed in this pull request:

• changed "ein Mark" to "eine Mark" in the test case ; code is fixed in #471

Status

• [X] READY
• [ ] HOLD
• [ ] WIP (Work-In-Progress)

How to verify this change

run test suite, esp. for lang = 'de' , currency = "DEM" , value = 1.00

Additional notes

I tried to make more substantial changes (the same should be done for other currencies named "Mark" like FIM, ... and for currencies named "Lira" (italian ITL [replaced by EUR], Turkish TRY and Syrian DMG) but since that didn't work out (mysterious errors) I try a minimal bug fix first.

[mrodriguezg1991]

@m-f-h Hello This change should be in the same PR where you updated the functionality, each PR is validated individually, so both changes can be validated together