[clang-tools-extra] [NFC][clang-tidy] Update documentation for StatusOr check. (PR #176498)

[Rohan Jacob-Rao via cfe-commits]

rohanjr wrote:

Checked formatting:
```
$ doc8 clang-tools-extra/docs/clang-tidy/checks/abseil/unchecked-statusor-access.rst
Scanning...
Validating...
========
Total files scanned = 1
Total files ignored = 0
Total accumulated errors = 0
Detailed error counts:
    - doc8.checks.CheckCarriageReturn = 0
    - doc8.checks.CheckIndentationNoTab = 0
    - doc8.checks.CheckMaxLineLength = 0
    - doc8.checks.CheckNewlineEndOfFile = 0
    - doc8.checks.CheckTrailingWhitespace = 0
    - doc8.checks.CheckValidity = 0
```

https://github.com/llvm/llvm-project/pull/176498