ci: Fix --index-state for hackage roundtrip tests

As a principle, tests which are required for CI to pass should be
reproducible and not depending on external resources changes or being
modified. The hackage tests currently violate this by depending on the
latest index state from hackage. This is problematic because until the
test is fixed all merges into master are blocked. Even though the
patches in question have nothing to do with the test.

It would be more suitable for a nightly job to run on the latest index
and for normal CI to run with a fixed index which is updated
periodically in a controlled manner.

Fixes #10284

validate.sh

@@ -417,14 +417,18 @@ CMD="$($CABALLISTBIN Cabal-tests:test:rpmvercmp) $TESTSUITEJOBS --hide-successes
 CMD="$($CABALLISTBIN Cabal-tests:test:no-thunks-test) $TESTSUITEJOBS --hide-successes"
 (cd Cabal-tests && timed $CMD) || exit 1
 
+
+# See #10284 for why this value is pinned.
+HACKAGE_TESTS_INDEX_STATE="--index-state=2024-08-25"
+
 CMD=$($CABALLISTBIN Cabal-tests:test:hackage-tests)
-(cd Cabal-tests && timed $CMD read-fields) || exit 1
+(cd Cabal-tests && timed $CMD read-fields $HACKAGE_TESTS_INDEX_STATE) || exit 1
 if $HACKAGETESTSALL; then
-    (cd Cabal-tests && timed $CMD parsec)    || exit 1
-    (cd Cabal-tests && timed $CMD roundtrip) || exit 1
+    (cd Cabal-tests && timed $CMD parsec $HACKAGE_TESTS_INDEX_STATE)    || exit 1
+    (cd Cabal-tests && timed $CMD roundtrip $HACKAGE_TESTS_INDEX_STATE) || exit 1
 else
-    (cd Cabal-tests && timed $CMD parsec d)    || exit 1
-    (cd Cabal-tests && timed $CMD roundtrip k) || exit 1
+    (cd Cabal-tests && timed $CMD parsec d $HACKAGE_TESTS_INDEX_STATE)    || exit 1
+    (cd Cabal-tests && timed $CMD roundtrip k $HACKAGE_TESTS_INDEX_STATE) || exit 1
 fi
 }