Handle GHC 9.8's x-partial warning, requires dropping GHC 7

[andreasabel]

Fixing a use of tail in the library. In the test-suite, tail [] is intended, so switch off the x-partial there.

Ignoring -Wx-partial on older GHCs requires -Wno-unrecognised-warning-flags, which entered GHC only in 8.0. Thus, dropping GHC 7.

Closes #56.

[andreasabel]

CI run on my fork: https://github.com/andreasabel/HUnit/pull/1

macos-latest fails due to:

• https://github.com/hspec/setup-haskell/issues/44

[sol]

CI run on my fork: andreasabel#1

macos-latest fails due to:

• hspec/setup-haskell broken on macos-latest (macos-14) setup-haskell#44

I think this can be fixed by using macos-12.

[sol]

If we drop support for GHC 7.* then there is some CPP that can be removed as well, e.g.

https://github.com/hspec/HUnit/blob/main/src/Test/HUnit/Lang.hs#L5

https://github.com/hspec/HUnit/blob/main/src/Test/HUnit/Base.hs#L6