Fix file extension of alignment-assumption-ignorelist.cppp test

During the renaming of blacklist to ignorelist this test got renamed
incorrectly.

Differential revision: https://reviews.llvm.org/D114710
diff --git a/compiler-rt/test/ubsan/TestCases/Pointer/alignment-assumption-ignorelist.cppp b/compiler-rt/test/ubsan/TestCases/Pointer/alignment-assumption-ignorelist.cpp
similarity index 100%
rename from compiler-rt/test/ubsan/TestCases/Pointer/alignment-assumption-ignorelist.cppp
rename to compiler-rt/test/ubsan/TestCases/Pointer/alignment-assumption-ignorelist.cpp