Drop support for Bazel 6.0.0

```
Error: no native function or rule 'package_relative_label'
```

Author: avdv

haskell/private/versions.bzl

@@ -14,7 +14,6 @@
 # because every bazel version tested requires a lot of space on CI
 # See https://github.com/tweag/rules_haskell/pull/1781#issuecomment-1187640454
 SUPPORTED_BAZEL_VERSIONS = [
-    "6.0.0",
     "6.3.2",
     "6.5.0",
     "7.1.0",

rules_haskell_tests/MODULE.bazel

@@ -119,7 +119,6 @@ use_repo(
     "asterius_bundle_linux_amd64",
     "bazel_6",
     "bazel_7",
-    "build_bazel_bazel_6_0_0",
     "build_bazel_bazel_6_3_2",
     "build_bazel_bazel_6_5_0",
     "build_bazel_bazel_7_1_0",