test: Fix test failures by specifying initial branch name in git init (#6872)

## What's the problem this PR addresses?
This PR adds --initial-branch=master option to ensure consistent test
behavior across different development environments.

Git has used main as the default branch for quite some time now, while
our tests expect master. When I ran the integration tests with my
default configuration (using main), they failed due to this mismatch.
This change ensures tests pass reliably regardless of local git
configuration and lowers the barrier to entry for new contributors!

Example error:

```bash
 FAIL  pkg-tests-specs/sources/commands/version/check.test.js (13.598 s)
  ● Commands › version check › it shouldn't detect a change when pulling master

    Temporary fixture folder: /private/var/folders/y2/dwrgd4rx32n7phb939mny5p00000gn/T/xfs-46e897df/test

    Command failed: git checkout master
    error: pathspec 'master' did not match any file(s) known to git


    ===== stdout:

    ```
    ```

    ===== stderr:

    ```
    error: pathspec 'master' did not match any file(s) known to git
    ```
```
<!-- Describe the rationale of your PR. -->
<!-- Link all issues that it closes. (Closes/Resolves #xxxx.) -->

...

## How did you fix it?

Explicitly set initial branch to master to ensure consistent test
behavior.
<!-- A detailed description of your implementation. -->

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Author: WooWan

packages/acceptance-tests/pkg-tests-core/sources/utils/exec.ts

@@ -62,7 +62,7 @@ export const execFile = (
 export const execGitInit = async (
   options: Options,
 ) => {
-  await execFile(`git`, [`init`], options);
+  await execFile(`git`, [`init`, `--initial-branch=master`], options);
   await execFile(`git`, [`config`, `user.email`, `[email protected]`], options);
   await execFile(`git`, [`config`, `user.name`, `Your Name`], options);
   await execFile(`git`, [`config`, `commit.gpgSign`, `false`], options);

packages/acceptance-tests/pkg-tests-specs/sources/commands/version/check.test.js

@@ -173,7 +173,7 @@ function makeVersionCheckEnv(cb) {
 
     await run(`install`);
 
-    await git(`init`, `.`);
+    await git(`init`, `--initial-branch=master`);
 
     // Otherwise we can't always commit
     await git(`config`, `user.name`, `John Doe`);