lib: re-enable doctests with ghc 8.10, to improve CI test

.github/workflows/test-linux-x64.yml

@@ -227,6 +227,7 @@ jobs:
     #     # --pedantic --no-run-benchmarks
     #   if: env.CONTINUE
 
+    # Note: doctests won't run if using GHC 9.0, see hledger-lib/package.yaml
     - name: Build all hledger modules fast, warning free, run unit/doc/bench tests
       env:
         stack: ${{ matrix.plan.stack }}

hledger-lib/package.yaml

@@ -171,9 +171,7 @@ tests:
 
     when:
     # disable doctest with GHC 9.0, https://github.com/sol/doctest/issues/301
-    #- condition: impl(ghc >= 9.0) && impl(ghc < 9.2)
-    # GHC 8.6 seems to be failing now also
-    - condition: impl(ghc < 9.2)
+    - condition: impl(ghc >= 9.0) && impl(ghc < 9.2)
       buildable: false
 
     # ghc 8.4+ on mac needs this workaround. See