perf(git_status): avoid running in bare repos

[wjhoward]

Description

This change adjusts the git_status module to no longer attempt to generate git_status for a bare repository as this is not possible when a repository does not have a work tree.

Motivation and Context

Currently entering a bare repository throws an error, as described in the associated issue.
Closes #5544

Screenshots (if appropriate):

When entering a bare repository the error is no longer visible:

How Has This Been Tested?

Locally by entering a bare repository as per the above screenshot.
You can also see the correct behaviour from the unit test output (I believe I've used the fixture correctly although not familiar with the setup):

cargo test --package starship --lib -- modules::git_status::tests::doesnt_generate_git_status_for_bare_repo --exact --nocapture
    Finished test [unoptimized + debuginfo] target(s) in 0.69s
     Running unittests src/lib.rs (target/debug/deps/starship-49403b2d84e0acbb)

running 1 test
[TRACE] - (starship::utils): Trying to read from "/Users/will/.config/starship.toml"
[TRACE] - (starship::utils): File read successfully
[TRACE] - (starship::config): Config file content: "
# ~/.config/starship.toml

[status]
style = 'bg:blue'
symbol = '🔴 '
success_symbol = '🟢 SUCCESS'
format = '[\[$symbol$common_meaning$signal_name$maybe_int\]]($style) '
map_symbol = true
disabled = false

"
[DEBUG] - (starship::config): Config parsed: {"status": Table({"style": String("bg:blue"), "symbol": String("🔴 "), "success_symbol": String("🟢 SUCCESS"), "format": String("[\\[$symbol$common_meaning$signal_name$maybe_int\\]]($style) "), "map_symbol": Boolean(true), "disabled": Boolean(false)})}
[TRACE] - (starship::context): Received completed pipestatus of None
[TRACE] - (starship::context): Found git repo: Repository { kind: Bare, git_dir: "/var/folders/zk/ctx002wn22l7tg0_rk4m_dyh0000gn/T/.tmp9ehSuN", work_dir: None }, (trust: Full)
[DEBUG] - (starship::modules::git_status): This is a bare repository, git_status is not applicable
[TRACE] - (starship::modules): Took 2.212191ms to compute module "git_status"
test modules::git_status::tests::doesnt_generate_git_status_for_bare_repo ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 1043 filtered out; finished in 0.07s

• I have tested using MacOS
• I have tested using Linux
• I have tested using Windows

Checklist:

• I have updated the documentation accordingly.
• I have updated the tests accordingly.