fix(git): set diff.noprefix=false for git diff to ensure correct format (#2174)

## Description

Parsing the output of git diff here depends on its exact format. The
user environment might be set up with diff.noprefix, in which case the
parsing fails, because the `a/` and `b/` prefixes for the paths is
missing. Passing `-c diff.noprefix=false` to the call overrides this.
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## Related Issue(s)

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lua/snacks/picker/source/git.lua

@@ -212,7 +212,9 @@ end
 ---@param opts snacks.picker.git.Config
 ---@type snacks.picker.finder
 function M.diff(opts, ctx)
-  local args = git_args(opts.args, "--no-pager", "diff", "--no-color", "--no-ext-diff")
+  local args = git_args(opts.args,
+    "-c", "diff.noprefix=false",
+    "--no-pager", "diff", "--no-color", "--no-ext-diff")
   local file, line ---@type string?, number?
   local header, hunk = {}, {} ---@type string[], string[]
   local header_len = 4