[clang] [clang][NFC]: Fix typo in comment in `ASTReader.h` (PR #202022)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-aarch64-quick` running on `linaro-clang-aarch64-quick` while building `clang` at step 5 "ninja check 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/65/builds/35469

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 5 (ninja check 1) failure: stage 1 checked (failure)
******************** TEST 'lit :: unsupported-cl.py' FAILED ********************
Exit Code: 2

Command Output (stdout):
--
# RUN: at line 3
env -u FILECHECK_OPTS "/usr/bin/python3.10" /home/tcwg-buildbot/worker/clang-aarch64-quick/llvm/llvm/utils/lit/lit.py -j1 -D use_normalized_slashes=0 --order=lexical --unsupported 'true.txt'    Inputs/xfail-cl/true.txt  | FileCheck --check-prefix=CHECK-UNSUPPORTED /home/tcwg-buildbot/worker/clang-aarch64-quick/stage1/utils/lit/tests/unsupported-cl.py
# executed command: env -u FILECHECK_OPTS /usr/bin/python3.10 /home/tcwg-buildbot/worker/clang-aarch64-quick/llvm/llvm/utils/lit/lit.py -j1 -D use_normalized_slashes=0 --order=lexical --unsupported true.txt Inputs/xfail-cl/true.txt
# executed command: FileCheck --check-prefix=CHECK-UNSUPPORTED /home/tcwg-buildbot/worker/clang-aarch64-quick/stage1/utils/lit/tests/unsupported-cl.py
# RUN: at line 7
env LIT_UNSUPPORTED='true.txt'  env -u FILECHECK_OPTS "/usr/bin/python3.10" /home/tcwg-buildbot/worker/clang-aarch64-quick/llvm/llvm/utils/lit/lit.py -j1 -D use_normalized_slashes=0 --order=lexical Inputs/xfail-cl/true.txt  | FileCheck --check-prefix=CHECK-UNSUPPORTED /home/tcwg-buildbot/worker/clang-aarch64-quick/stage1/utils/lit/tests/unsupported-cl.py
# executed command: env LIT_UNSUPPORTED=true.txt env -u FILECHECK_OPTS /usr/bin/python3.10 /home/tcwg-buildbot/worker/clang-aarch64-quick/llvm/llvm/utils/lit/lit.py -j1 -D use_normalized_slashes=0 --order=lexical Inputs/xfail-cl/true.txt
# .---command stderr------------
# | lit.py: /home/tcwg-buildbot/worker/clang-aarch64-quick/llvm/llvm/utils/lit/lit/TestTimes.py:29: fatal: found malformed timing data in '/home/tcwg-buildbot/worker/clang-aarch64-quick/stage1/utils/lit/tests/Inputs/xfail-cl/.lit_test_times.txt'; remove the file to regenerate it
# `-----------------------------
# error: command failed with exit status: 2
# executed command: FileCheck --check-prefix=CHECK-UNSUPPORTED /home/tcwg-buildbot/worker/clang-aarch64-quick/stage1/utils/lit/tests/unsupported-cl.py
# .---command stderr------------
# | FileCheck error: '<stdin>' is empty.
# | FileCheck command line:  FileCheck --check-prefix=CHECK-UNSUPPORTED /home/tcwg-buildbot/worker/clang-aarch64-quick/stage1/utils/lit/tests/unsupported-cl.py
# `-----------------------------
# error: command failed with exit status: 2

--

********************


```

</details>

https://github.com/llvm/llvm-project/pull/202022