Gradle build fix. CI Flutter version upgrade

[SaintKiri]

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• If you made changes to the code:
  • I added new tests to check the change I am making or feature I am adding.
  • All existing and new tests are passing.

[proninyaroslav]

Please try to change flutter sdk version

[proninyaroslav]

Oh, sorry. This looks like a linter error. If you could fix it in the code, that would be great. If not, I can accept it as is.

[SaintKiri]

Ok let me work on that a bit more.

[SaintKiri]

I've cleared all linting related issue (from output of flutter analyze). Tests are all passing. On my fork, all CI tests are passing.

However, I haven't look into details about workmanager's debug field. I simply removed all variables around isInDebugMode. I ran the build just fine in an android emulator.

@proninyaroslav If you want, you can merge this PR just for the sake of suppressing the lint. I will work on workmanager in another time.

[proninyaroslav]

Thank you