refactor(upgrade): use centralized user-agent for GitHub API requests

[BYK]

Summary

Replace hardcoded User-Agent: sentry-cli in the upgrade module with the centralized getUserAgent() function from constants.ts.

This ensures GitHub API requests (for version checks and releases) use the same descriptive user-agent format as Sentry API requests:

sentry-cli/0.5.0 (linux-x64) bun/1.3.3

Changes

• Import getUserAgent() from constants.ts
• Convert static GITHUB_HEADERS constant to getGitHubHeaders() function
• Update fetchLatestFromGitHub() and versionExists() to use the new function

Closes: N/A

^{Cursor Bugbot reviewed your changes and found no issues for commit 6189f50}

[github-actions]

Semver Impact of This PR

🟢 Patch (bug fixes)

📋 Changelog Preview

This is how your changes will appear in the changelog.
Entries from this PR are highlighted with a left border (blockquote style).

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New Features ✨

• (dsn) Add project root detection for automatic DSN discovery by BYK in #159
• (issue) Replace --org/--project flags with /ID syntax by BYK in #161
• (telemetry) Add withTracing helper to reduce Sentry span boilerplate by BYK in #172

Bug Fixes 🐛

• (types) Align schema types with Sentry API by betegon in #169
• Added nullable in substatus's zod validation by MathurAditya724 in #157

Internal Changes 🔧

• (upgrade) Use centralized user-agent for GitHub API requests by BYK in #173

Other

• test: add model-based and property-based testing with fast-check by BYK in #166

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_{🤖 This preview updates automatically when you update the PR.}

[github-actions]

Codecov Results 📊

✅ Patch coverage is 100.00%. Project has 2184 uncovered lines.
✅ Project coverage is 70.49%. Comparing base (base) to head (head).

Files with missing lines (34)

File	Patch %	Lines
human.ts	31.80%	⚠️ 684 Missing
resolve-target.ts	10.74%	⚠️ 291 Missing
oauth.ts	25.10%	⚠️ 194 Missing
upgrade.ts	40.23%	⚠️ 153 Missing
api-client.ts	74.21%	⚠️ 138 Missing
resolver.ts	3.23%	⚠️ 120 Missing
errors.ts	5.94%	⚠️ 95 Missing
migration.ts	47.44%	⚠️ 82 Missing
version-check.ts	34.04%	⚠️ 62 Missing
telemetry.ts	66.89%	⚠️ 50 Missing
api.ts	89.80%	⚠️ 47 Missing
seer.ts	75.54%	⚠️ 45 Missing
preload.ts	38.71%	⚠️ 38 Missing
seer.ts	79.87%	⚠️ 30 Missing
schema.ts	52.73%	⚠️ 26 Missing
utils.ts	87.43%	⚠️ 24 Missing
detector.ts	90.10%	⚠️ 20 Missing
code-scanner.ts	95.06%	⚠️ 16 Missing
project-root.ts	97.00%	⚠️ 11 Missing
fs-utils.ts	57.14%	⚠️ 9 Missing
auth.ts	94.78%	⚠️ 7 Missing
dsn-cache.ts	96.71%	⚠️ 7 Missing
feedback.ts	84.21%	⚠️ 6 Missing
arg-parsing.ts	93.41%	⚠️ 6 Missing
upgrade.ts	93.83%	⚠️ 5 Missing
colors.ts	91.84%	⚠️ 4 Missing
env-file.ts	97.58%	⚠️ 3 Missing
sentry-urls.ts	88.00%	⚠️ 3 Missing
project-aliases.ts	97.40%	⚠️ 2 Missing
project-root-cache.ts	96.92%	⚠️ 2 Missing
alias.ts	99.28%	⚠️ 1 Missing
parser.ts	98.63%	⚠️ 1 Missing
helpers.ts	94.74%	⚠️ 1 Missing
helpers.ts	94.74%	⚠️ 1 Missing

Coverage diff

@@            Coverage Diff             @@
##          main       #PR       +/-##
==========================================
+ Coverage    70.49%    70.49%        —%
==========================================
  Files           54        54         —
  Lines         7400      7402        +2
  Branches         0         0         —
==========================================
+ Hits          5216      5218        +2
- Misses        2184      2184         —
- Partials         0         0         —

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