Temporarily disable backport linter

[pratikunterwegs]

This issue is to flag that {lintr} throws confusing warnings from the backport linter when encountering a dependency on R >= 2.10, which causes the lint-changed-files workflow to fail.

This is temporarily fixed by

• Disabling the backport linter in .lintr
• Re-enabling backport linter in .lintr once {lintr} issue is fixed

[pratikunterwegs]

Part 1 completed in #183

[pratikunterwegs]

This issue persists as of June 2024.