hackport.cabal: Fix doctest-v2

build-tool-depends doesn't play nice with Setup.hs installs, and tries
to rebuild cabal-install/doctest locally. This has recently caused some
compilation errors when it tries to build cabal-install, so we'll just
remove it from build-tool-depends on the assumption that whoever is
running doctest-v2 probably has /usr/bin/cabal on their system.

All Cabal versions except 3.8 fail on GitHub tests complaining that they
cannot build ghc:

```
cabal: Failed to build ghc-8.10.7 (which is required by exe:doctest from
doctest-0.21.1)
```

This reverts commit 51bc8c1.

See: gentoo-haskell/gentoo-haskell#1074
See: haskell/cabal#8434
Signed-off-by: hololeap <[email protected]>

Author: hololeap

.github/workflows/haskell.yml

@@ -14,7 +14,6 @@ jobs:
       matrix:
         cabal:
           [ "3.4"
-          , "3.6"
           , "3.8"
           ]
         ghc:
@@ -61,5 +60,5 @@ jobs:
         cabal build --only-dependencies
     - name: Build
       run: cabal build
-    - name: Run spec test
-      run: cabal test --test-option=--color --test-show-details=streaming spec
+    - name: Run all enabled tests
+      run: cabal test --test-option=--color --test-show-details=streaming

hackport.cabal

@@ -1026,9 +1026,6 @@ test-suite doctests
 
 test-suite doctests-v2
   import:             warnings
-  -- doctests-v2 is causing problems, looking for ghc lib and alex on
-  -- github CI. This may be fixable.
-  buildable:          False
   type:               exitcode-stdio-1.0
   default-language:   Haskell98
   hs-source-dirs:     tests/doctests-v2
@@ -1038,7 +1035,7 @@ test-suite doctests-v2
     , process
 
   build-tool-depends:
-    , cabal-install:cabal  >=3.4
+    -- cabal-install should already be installed if this is being built...
     , doctest:doctest      >=0.8
 
   if flag(cabal-v1)