use clang-17 since gcc doesn't have FSan (and that's the default)

Author: NattyNarwhal

Diff for: .github/workflows/nightly.yml

@@ -57,6 +57,8 @@ jobs:
           configurationParameters: >-
             CFLAGS="-fsanitize=undefined,address -fno-sanitize=function -DZEND_TRACK_ARENA_ALLOC"
             LDFLAGS="-fsanitize=undefined,address -fno-sanitize=function"
+            CC=clang-17
+            CXX=clang++-17
             --enable-debug
             --enable-zts
           skipSlow: true # FIXME: This should likely include slow extensions