add FirebaseAppCheckKtxRegistrar to appcheck-ktx

[thatfiredev]

This PR should add the missing KtxRegistrar to appcheck-ktx

[google-oss-bot]

Coverage Report ¹

Affected Products

No changes between base commit (d40db69) and merge commit (c8b4daa).

Test Logs

• Base (d40db69): https://github.com/firebase/firebase-android-sdk/actions/runs/2877037989
• Merge (c8b4daa): https://github.com/firebase/firebase-android-sdk/actions/runs/2877216133

Notes

• Commit (c8b4daa) is created by Prow via merging PR base commit (d40db69) and head commit (9080c15).
• Run gradle <product>:checkCoverage to produce HTML coverage reports locally. After gradle commands finished, report files can be found under <product-build-dir>/reports/jacoco/.

1. https://storage.googleapis.com/firebase-sdk-metric-reports/dFPEof5bZG.html

[github-actions]

Unit Test Results

0 files   -    391  0 suites   - 391   0s ⏱️ - 45m 56s
0 tests  - 4 707  0 ✔️  - 4 652  0 💤  - 22  0 ❌  - 33 
0 runs   - 4 723  0 ✔️  - 4 668  0 💤  - 22  0 ❌  - 33 

Results for commit 9080c15. ± Comparison against base commit eb4d215.

♻️ This comment has been updated with latest results.

[google-oss-bot]

Size Report ¹

Affected Products

• firebase-appcheck-ktx

  Type	Base (d40db69)	Merge (c8b4daa)	Diff
  aar	5.60 kB	6.44 kB	+839 B (+15.0%)
  apk (aggressive)	350 kB	351 kB	+88 B (+0.0%)
  apk (release)	1.52 MB	1.52 MB	+232 B (+0.0%)

Test Logs

• Base (d40db69): https://github.com/firebase/firebase-android-sdk/actions/runs/2877037989
• Merge (c8b4daa): https://github.com/firebase/firebase-android-sdk/actions/runs/2877216133

Notes

• Commit (c8b4daa) is created by Prow via merging PR base commit (d40db69) and head commit (9080c15).

1. https://storage.googleapis.com/firebase-sdk-metric-reports/qBgpllHTBH.html

[vkryachko]

Thanks for the fix 👍

One minor nit below

[google-oss-bot]

@thatfiredev: The following test failed, say /retest to rerun them all:

Test name	Commit	Details	Rerun command
smoke-tests	9080c15	link	/test smoke-tests

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