BUG: git grep behave oddly with alternatives

[Marco Nenciarini <marco.nenciarini@enterprisedb.com>]

I've installed latest git from brew and suddenly git grep started 
behaving oddly when using alternatives.

```
$ echo abd > test.file
$ git grep --untracked 'a\(b\|c\)d' test.file
$ git grep --untracked 'a\(b\)d' test.file
test.file:abd
```

It should have matched in both cases.


If I switch to exented pattern it starts working again

```
$ git grep --untracked -E 'a(b|c)d' test.file
test.file:abd
```

[System Info]
git version:
git version 2.39.0
cpu: x86_64
no commit associated with this build
sizeof-long: 8
sizeof-size_t: 8
shell-path: /bin/sh
feature: fsmonitor--daemon
uname: Darwin 22.2.0 Darwin Kernel Version 22.2.0: Fri Nov 11 02:08:47 
PST 2022; root:xnu-8792.61.2~4/RELEASE_X86_64 x86_64
compiler info: clang: 14.0.0 (clang-1400.0.29.202)
libc info: no libc information available
$SHELL (typically, interactive shell): /usr/local/bin/bash


-- 
Marco Nenciarini - EnterpriseDB
marco.nenciarini@enterprisedb.com | www.enterprisedb.com