CI: Work around cabal issues

This adds a Haskell-CI patch file containing workarounds for the following
`cabal` issues when building with `head.hackage` + GHC 9.12:

* haskell/cabal#6522: Remove the use of
  `head.hackage.ghc.haskell.org:override` in the `cabal` configuration file so
  that `ghc-paths`' custom `Setup.hs` script can find a suitable `Cabal`
  version.

* haskell/cabal#10500: Remove the use of
  `allow-newer: *:Cabal *:Cabal-syntax` in the generated `cabal.project` file.

We should be able to remove this patch file once we no longer depend on the use
of `head.hackage`, as well as when Haskell-CI upgrades to use
`cabal-install-3.14`.

.github/workflows/haskell-ci.yml

@@ -184,7 +184,7 @@ jobs:
                         26021a13b401500c8eb2761ca95c61f2d625bfef951b939a8124ed12ecf07329
                         f76d08be13e9a61a377a85e2fb63f4c5435d40f8feb3e12eb05905edb8cdea89
              key-threshold: 3
-          active-repositories: hackage.haskell.org, head.hackage.ghc.haskell.org:override
+          active-repositories: hackage.haskell.org
           EOF
           fi
           cat >> $CABAL_CONFIG <<EOF
@@ -261,7 +261,7 @@ jobs:
             tag:      730a0ed799c91324d42b70d3780d6b3215cafc3c
           EOF
           if $HEADHACKAGE; then
-          echo "allow-newer: $($HCPKG list --simple-output | sed -E 's/([a-zA-Z-]+)-[0-9.]+/*:\1,/g')" >> cabal.project
+          echo "$($HCPKG list --simple-output | xargs -d' ' -n 1 | grep -v "^Cabal" | sed -E 's/([a-zA-Z-]+)-[0-9.]+/allow\-newer\: *:\1/g')" >> cabal.project
           fi
           $HCPKG list --simple-output --names-only | perl -ne 'for (split /\s+/) { print "constraints: any.$_ installed\n" unless /^(Cabal|Cabal-syntax|singletons|singletons-base|singletons-base-code-generator|singletons-th)$/; }' >> cabal.project.local
           cat cabal.project

cabal.haskell-ci

@@ -6,3 +6,6 @@ jobs-selection:         any
 haddock-components:     libs
 -- Needed to avoid https://github.com/haskell/cabal/issues/9917
 installed:              +all -Cabal -Cabal-syntax
+-- Needed to work around https://github.com/haskell/cabal/issues/6522 and
+-- https://github.com/haskell/cabal/issues/10500
+github-patches:         github.yml.patch

github.yml.patch

@@ -0,0 +1,22 @@
+diff --git a/.github/workflows/haskell-ci.yml b/.github/workflows/haskell-ci.yml
+index 55fb206..c9db909 100644
+--- a/.github/workflows/haskell-ci.yml
++++ b/.github/workflows/haskell-ci.yml
+@@ -184,7 +184,7 @@ jobs:
+                         26021a13b401500c8eb2761ca95c61f2d625bfef951b939a8124ed12ecf07329
+                         f76d08be13e9a61a377a85e2fb63f4c5435d40f8feb3e12eb05905edb8cdea89
+              key-threshold: 3
+-          active-repositories: hackage.haskell.org, head.hackage.ghc.haskell.org:override
++          active-repositories: hackage.haskell.org
+           EOF
+           fi
+           cat >> $CABAL_CONFIG <<EOF
+@@ -261,7 +261,7 @@ jobs:
+             tag:      730a0ed799c91324d42b70d3780d6b3215cafc3c
+           EOF
+           if $HEADHACKAGE; then
+-          echo "allow-newer: $($HCPKG list --simple-output | sed -E 's/([a-zA-Z-]+)-[0-9.]+/*:\1,/g')" >> cabal.project
++          echo "$($HCPKG list --simple-output | xargs -d' ' -n 1 | grep -v "^Cabal" | sed -E 's/([a-zA-Z-]+)-[0-9.]+/allow\-newer\: *:\1/g')" >> cabal.project
+           fi
+           $HCPKG list --simple-output --names-only | perl -ne 'for (split /\s+/) { print "constraints: any.$_ installed\n" unless /^(Cabal|Cabal-syntax|singletons|singletons-base|singletons-base-code-generator|singletons-th)$/; }' >> cabal.project.local
+           cat cabal.project