Auto merge of #26720 - camelid:real-version-hash, r=SimonSapin

Show the real commit hash for `./servo --version`, not the bundle hash

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Show the real commit hash of the build when run on a bundle commit, rather than showing the bundle's hash.

It gets the real commit hash by extracting it from the bundle commit message, which has the form `Shallow version of commit {sha1}`, where `{sha1}` is the real commit hash.

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `___` with appropriate data: -->
- [x] `./mach build -d` does not report any errors (edits Python code, no Rust changes)
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #26386 (GitHub issue number if applicable)

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- [ ] There are tests for these changes OR
- [X] These changes do not require tests because this only changes infrastructure

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python/servo/command_base.py

@@ -734,9 +734,28 @@ install them, let us know by filing a bug!")
 
         git_info = []
         if os.path.isdir('.git') and is_build:
-            git_sha = subprocess.check_output([
-                'git', 'rev-parse', '--short', 'HEAD'
+            # Get the subject of the commit
+            git_commit_subject = subprocess.check_output([
+                'git', 'show', '-s', '--format=%s', 'HEAD'
             ]).strip()
+
+            git_sha = None
+            # Check if it's a bundle commit
+            if git_commit_subject.startswith(b"Shallow version of commit "):
+                # This is a bundle commit
+                # Get the SHA-1 from the bundle subject: "Shallow version of commit {sha1}"
+                git_sha = git_commit_subject.split(b' ')[-1].strip()
+                # Shorten hash
+                # NOTE: Partially verifies the hash, but it will still pass if it's, e.g., a tree
+                git_sha = subprocess.check_output([
+                    'git', 'rev-parse', '--short', git_sha
+                ])
+            else:
+                # This is a regular commit
+                git_sha = subprocess.check_output([
+                    'git', 'rev-parse', '--short', 'HEAD'
+                ]).strip()
+
             git_is_dirty = bool(subprocess.check_output([
                 'git', 'status', '--porcelain'
             ]).strip())