Remove `x-partial` from `-Wdefault`

GHC 9.8.1's new x-partial warning (currently warning about head and tail) is a hlint-style warning and should not be on by default.

While it is possible to switch it off in .cabal files, GHC is also used a lot in teaching where one works with small Haskell scripts without going through the effort of making a cabal file for each of these.

Here is an example for teaching material that uses head: https://github.com/teach-afp/afp-code/blob/f39715a6dfa81fde74d8043f0880e0b626da0f7d/L1/Lect1.hs#L102-L107

testLazy2 = head [3, undefined, 17]
testLazy3 = head (3:4:error "no tail")
testLazy4 = head [error "no first elem", 17, 13]
testLazy5 = head (error "no list at all")

Running this interactively (e.g. with haskell-mode in Emacs) my session is spammed with 4 instances of

Lect1.hs:114:13-16: warning: [GHC-63394] [-Wx-partial] …
    In the use of ‘head’
    (imported from Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."

The warning seems resistant to efforts to disable, like :seti -Wno-x-partial in GHCi:

ghci> :seti -Wno-x-partial
ghci> :r
[1 of 1] Compiling Lect1            ( Lect1.hs, interpreted ) [Source file changed]

Lect1.hs:112:13: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
112 | testLazy2 = head [3, undefined, 17]
    |             ^^^^

Lect1.hs:113:13: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
113 | testLazy3 = head (3:4:error "no tail")
    |             ^^^^

Lect1.hs:114:13: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
114 | testLazy4 = head [error "no first elem", 17, 13]
    |             ^^^^

Lect1.hs:115:13: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
115 | testLazy5 = head (error "no list at all")
    |             ^^^^
Ok, one module loaded.

Update: :set -Wno-x-partial is required and works for disabling the warning for file content that is loaded interactively.