fix(picker.git): add ignorecase for git_grep (#1629)

## Description
Add option for `ignorecase` for `git_grep`
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maintainers
  why we should accept this pull request. -->

## Related Issue(s)
Fixes #1627
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  If this PR fixes any issues, please link to the issue here.
  - Fixes #<issue_number>
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## Screenshots

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lua/snacks/picker/config/sources.lua

@@ -256,6 +256,7 @@ M.git_files = {
 ---@field untracked? boolean search in untracked files
 ---@field submodules? boolean search in submodule files
 ---@field need_search? boolean require a search pattern
+---@field ignorecase? boolean ignore case
 M.git_grep = {
   finder = "git_grep",
   format = "file",

lua/snacks/picker/source/git.lua

@@ -54,6 +54,9 @@ function M.grep(opts, ctx)
   elseif opts.submodules then
     table.insert(args, "--recurse-submodules")
   end
+  if opts.ignorecase then
+    table.insert(args, "-i")
+  end
   table.insert(args, ctx.filter.search)
   if not opts.cwd then
     opts.cwd = Snacks.git.get_root() or uv.cwd() or "."