- Prefer Breaks+Replaces over Conflicts+Replaces in debian/control.

- Clean away conflict/break/replace with self as it either has no
  effect or harmfully prevents upgrades to self (packages from this
  source version).

- Remove references to mariadb-server-10.11 as the package names no
  longer have versions and thus such references are unnecessary cruft.

- Apply 'wrap-and-sort -av' and minor typo fixing.

- Extend Salsa-CI to test for upgrades from 10.9 and 10.10 to 10.11.

- Add minimal required new Lintian overrides so Salsa-CI would not
  fail on Lintian.