[clang-tidy] Avoid checking magic numbers if _BitInt (#65888)

Recent changes to add _BitInt support have caused our internal random
testing to fail. This change just avoids a readability magic numbers
check for now if a _BitInt. The crash seen (edited for clarity) is shown
below.

<src-root>/llvm/include/llvm/ADT/APInt.h:1488:
  uint64_t llvm::APInt::getZExtValue() const: Assertion `getActiveBits()
  <= 64 && "Too many bits for uint64_t"' failed.

...
 #9 <address> llvm::APInt::getZExtValue() const
      <src-root>/llvm/include/llvm/ADT/APInt.h:1488:5
      clang::IntegerLiteral const*) const

<src-root>/clang-tools-extra/clang-tidy/readability/MagicNumbersCheck.cpp:198:47
<clang::IntegerLiteral>(clang::ast_matchers::MatchFinder::MatchResult
      const&, char const*)

<src-root>/clang-tools-extra/clang-tidy/readability/MagicNumbersCheck.h:67:5
      clang::ast_matchers::MatchFinder::MatchResult const&)

<src-root>/clang-tools-extra/clang-tidy/readability/MagicNumbersCheck.cpp:152:35
...

Reviewed By: donat.nagy