fix(GitHub Integration): Fix JWT generation for GitHub API calls

[emyller]

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Changes

Closes #6979

All GitHub integration API calls fail with TypeError: Issuer (iss) must be a string. (FLAGSMITH-API-5K9).

Our GITHUB_APP_ID setting is an integer. PyGithub 2.1.1 passes it directly to the JWT iss claim, which worked until #6950 bumped PyJWT to 2.12.0 — a version that validates iss as a string per RFC 7519.

PyGithub already fixed this in v2.7.0 by converting app_id to string internally. This PR upgrades PyGithub to ~2.8 and adds an explicit str() call in our code as a safeguard.

How did you test this code?

New unit tests exercising the full PyGithub + PyJWT stack.

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3 Skipped Deployments

Project	Deployment	Actions	Updated (UTC)
docs	Ignored	Preview	Mar 18, 2026 8:50pm
flagsmith-frontend-preview	Ignored	Preview	Mar 18, 2026 8:50pm
flagsmith-frontend-staging	Ignored	Preview	Mar 18, 2026 8:50pm

[github-actions]

Docker builds report

Image	Build Status	Security report
ghcr.io/flagsmith/flagsmith-e2e:pr-6983	Finished ✅	Skipped
ghcr.io/flagsmith/flagsmith-api-test:pr-6983	Finished ✅	Skipped
ghcr.io/flagsmith/flagsmith-frontend:pr-6983	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith:pr-6983	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith-private-cloud:pr-6983	Finished ✅	Results ✅

[github-actions]

Playwright Test Results (oss - depot-ubuntu-latest-arm-16)

 10 passed

Details

 10 tests across 7 suites
 27.5 seconds
 a870a81
 🔄 Run: #15362 (attempt 1)

Playwright Test Results (oss - depot-ubuntu-latest-16)

 10 passed

Details

 10 tests across 7 suites
 49.1 seconds
 a870a81
 🔄 Run: #15362 (attempt 1)

Playwright Test Results (private-cloud - depot-ubuntu-latest-arm-16)

 16 passed

Details

 16 tests across 13 suites
 55.6 seconds
 a870a81
 🔄 Run: #15362 (attempt 1)

Playwright Test Results (private-cloud - depot-ubuntu-latest-16)

 2 passed

Details

 2 tests across 2 suites
 1 minute, 4 seconds
 a870a81
 🔄 Run: #15362 (attempt 1)

Playwright Test Results (oss - depot-ubuntu-latest-16)

 10 passed

Details

 10 tests across 7 suites
 49.7 seconds
 c695180
 🔄 Run: #15363 (attempt 1)

Playwright Test Results (oss - depot-ubuntu-latest-arm-16)

 10 passed

Details

 10 tests across 7 suites
 46.7 seconds
 c695180
 🔄 Run: #15363 (attempt 1)

Playwright Test Results (private-cloud - depot-ubuntu-latest-16)

 16 passed

Details

 16 tests across 13 suites
 1 minute, 2 seconds
 c695180
 🔄 Run: #15363 (attempt 1)

Playwright Test Results (private-cloud - depot-ubuntu-latest-arm-16)

 16 passed

Details

 16 tests across 13 suites
 39.2 seconds
 c695180
 🔄 Run: #15363 (attempt 1)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.31%. Comparing base (332df52) to head (c695180).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6983   +/-   ##
=======================================
  Coverage   98.31%   98.31%           
=======================================
  Files        1334     1335    +1     
  Lines       49748    49782   +34     
=======================================
+ Hits        48911    48945   +34     
  Misses        837      837           

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