Fall back to GHC 8.6.5 on Windows

GHC 8.8.3 is broken on Windows CI due to
https://gitlab.haskell.org/ghc/ghc/issues/17926

constants.bzl

@@ -1,2 +1,17 @@
-test_ghc_version = "8.8.3"
-test_stack_snapshot = "lts-15.4"
+load("@os_info//:os_info.bzl", "is_linux", "is_nix_shell", "is_windows")
+
+# Windows builds fail with the following error on CI
+#
+#   Access violation in generated code when writing 0x0
+#
+#    Attempting to reconstruct a stack trace...
+#
+#      Frame	Code address
+#    * 0x461dab0	0x37f7b66 C:\users\vssadministrator\_bazel_vssadministrator\w3d6ug6o\execroot\rules_haskell\external\rules_haskell_ghc_windows_amd64\bin\ghc.exe+0x33f7b66
+#    * 0x461dab8	0x3277bb9 C:\users\vssadministrator\_bazel_vssadministrator\w3d6ug6o\execroot\rules_haskell\external\rules_haskell_ghc_windows_amd64\bin\ghc.exe+0x2e77bb9
+#    * 0x461dac0	0x3
+#
+# This seems to be an instance of https://gitlab.haskell.org/ghc/ghc/issues/17926.
+# Until a fix is released we fall back to an older GHC release on Windows.
+test_ghc_version = "8.8.3" if not is_windows else "8.6.5"
+test_stack_snapshot = "lts-15.4" if not is_windows else "lts-14.4"