Only consider version constraints with --reject-unconstrained-dependenies

[philderbeast]

Fixes #12190.

I'll squash commits before applying the merge label if this pull request is approved.

Manual QA Notes

Compare running the included package test with the version of cabal-install:exe:cabal from this branch and with a released version, such as cabal-3.16.1.0.

Run the test locally manually, it should pass.

$ ghc --numeric-version
9.14.1

$ cabal build all --enable-tests

$ cabal run cabal-testsuite:cabal-tests -- \
  --with-cabal=./dist-newstyle/build/x86_64-linux/ghc-9.14.1/cabal-install-3.19.0.0/x/cabal/build/cabal/cabal \
  cabal-testsuite/PackageTests/RequireExplicit/FlagNotVersion/cabal.test.hs --accept
  
$ echo $status
0

Run the test with a released version of cabal and it should fail:

$ cabal run cabal-testsuite:cabal-tests -- \
   --with-cabal=/home/.../.ghcup/bin/cabal \
   cabal-testsuite/PackageTests/RequireExplicit/FlagNotVersion/cabal.test.hs --accept
  
$ echo $status
1

Modify the test so that it will succeed for versions of cabal without this fix.

Tip

You may need to delete the named tests too that were added (appended) after these instructions.

$ diff --git a/cabal-testsuite/PackageTests/RequireExplicit/FlagNotVersion/cabal.test.hs b/cabal-testsuite/PackageTests/RequireExplicit/FlagNotVersion/cabal.test.hs
index 01f7429c1..4a617d2b1 100644
--- a/cabal-testsuite/PackageTests/RequireExplicit/FlagNotVersion/cabal.test.hs
+++ b/cabal-testsuite/PackageTests/RequireExplicit/FlagNotVersion/cabal.test.hs
@@ -1,4 +1,3 @@
 import Test.Cabal.Prelude
 main = cabalTest . recordMode RecordMarked $ withRepo "repo" $ do
-  res <- fails $ cabal' "v2-build" ["all", "--dry-run"]
-  assertOutputContains "not a user-provided goal" res
+  cabal "v2-build" ["all", "--dry-run"]

Run the test with a released version of cabal and observe the change in output:

$ cabal run cabal-testsuite:cabal-tests -- \
   --with-cabal=/home/.../.ghcup/bin/cabal \
   cabal-testsuite/PackageTests/RequireExplicit/FlagNotVersion/cabal.test.hs --accept

The change of output:

$ git diff
diff --git a/cabal-testsuite/PackageTests/RequireExplicit/FlagNotVersion/cabal.out b/cabal-testsuite/PackageTests/RequireExplicit/FlagNotVersion/cabal.out
index a3a5898e7..215cadb23 100644
--- a/cabal-testsuite/PackageTests/RequireExplicit/FlagNotVersion/cabal.out
+++ b/cabal-testsuite/PackageTests/RequireExplicit/FlagNotVersion/cabal.out
@@ -5,10 +5,7 @@
 Downloading the latest package list from test-local-repo
 # cabal v2-build
 Resolving dependencies...
-Error: [Cabal-7107]
-Could not resolve dependencies:
-[__0] trying: a-0 (user goal)
-[__1] next goal: some-lib (dependency of a)
-[__1] fail (not a user-provided goal nor mentioned as a constraint, but reject-unconstrained-dependencies was set)
-[__1] fail (backjumping, conflict set: a, some-lib)
-After searching the rest of the dependency tree exhaustively, these were the goals I've had most trouble fulfilling: a (2), some-lib (1)
+Build profile: -w ghc-<GHCVER> -O1
+In order, the following would be built:
+ - some-lib-1.0 (lib) (requires build)
+ - a-0 (lib) (first run)

---

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