allow haskell-src-exts-1.15

(cherry picked from commit d2ba3288033940efb44dbe0a555808f16d822857)
Bump version to 0.2.2.6
Release notes for 0.2.2.6

(cherry picked from commit 43f677b139bbb931efbe6c17adb2bc1fb91d7b4e)