[clang-tidy] Fix cert-err33-c to ignore functions with same prefixes as target (#135160)

PR #82952 introduced regex matching for `CheckedFunctions` in
`UnusedReturnValueCheck` which is used by the checker `cert-err33-c`.

Add a testcase and fix false positives by adding end-of-string to target
regex's.

---------

Signed-off-by: Björn Svensson <bjorn.a.svensson@est.tech>

clang-tools-extra/docs/ReleaseNotes.rst

@@ -151,6 +151,10 @@ Changes in existing checks
   <clang-tidy/checks/bugprone/unsafe-functions>` check to allow specifying
   additional C++ member functions to match.
 
+- Improved :doc:`cert-err33-c
+  <clang-tidy/checks/cert/err33-c>` check by fixing false positives when
+  a function name is just prefixed with a targeted function name.
+
 - Improved :doc:`misc-const-correctness
   <clang-tidy/checks/misc/const-correctness>` check by adding the option
   `AllowedTypes`, that excludes specified types from const-correctness