perf(git): invoke git status with --no-optional-locks (#2175)

## Description

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maintainers
  why we should accept this pull request. -->
According to the Git docs, `git status` automatically refreshes the
index, meaning it recreates the `.git/index` file. In `watch.lua`, we
specifically watch for modifications of that file and (indirectly?) run
`git status` everytime it changes. This effectively forms an infinite
loop of refreshes whenever the explorer is open.

Passing `--no-optional-locks` to `git status` breaks this loop because
it stops it from refreshing the index. Doing this also happens to be the
official recommendation for scripts doing `git status` in the
background: https://git-scm.com/docs/git-status#_background_refresh

## Related Issue(s)

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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/explorer/git.lua

@@ -61,6 +61,7 @@ function M.update(cwd, opts)
     hide = true,
     args = {
       "--no-pager",
+      "--no-optional-locks",
       "status",
       "--porcelain=v1",
       "--ignored=matching",