Running unit tests changes wallet.db file committed into the repo

[starius]

Running make unit modifies file cmd/chantools/testdata/wallet.db:

$ make unit
...
$ git diff
diff --git a/cmd/chantools/testdata/wallet.db b/cmd/chantools/testdata/wallet.db
index 4317346..ceb8d63 100644
Binary files a/cmd/chantools/testdata/wallet.db and b/cmd/chantools/testdata/wallet.db differ

This results in unwanted updates of the file, unrelated to a change.

I propose to change the unit test to copy a file to temp directory first and to run the modifications needed for the test on the temp file.

[guggero]

Yeah, I'm aware of that unfortunate side effect. I usually just reverted the change before committing, which isn't great 😅