Bump mnemonic from 0.20 to 0.21

Bumps [mnemonic](https://github.com/trezor/python-mnemonic) from 0.20 to 0.21.
- [Changelog](https://github.com/trezor/python-mnemonic/blob/master/CHANGELOG.rst)
- [Commits](trezor/python-mnemonic@v0.20...v0.21)

---
updated-dependencies:
- dependency-name: mnemonic
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

requirements.txt

@@ -23,7 +23,7 @@ youtube-search-python==1.6.6
 token-bucket==0.3.0
 coloredlogs==15.0.1
 tronpy==0.4.0
-mnemonic==0.20
+mnemonic==0.21
 qrcode==7.4.2
 blinker==1.7.0
 flask===3.0.0