Disable shebangless script tests in CI with sanitizers

Sanitizers inject a busted posix_spawn interceptor which mishandles
shebangless scripts. Disable this test under sanitizers.

.github/workflows/main.yml

@@ -84,6 +84,7 @@ jobs:
         make
     - name: make test
       env:
+          FISH_CI_SAN: 1
           ASAN_OPTIONS: check_initialization_order=1:detect_stack_use_after_return=1:detect_leaks=1
           UBSAN_OPTIONS: print_stacktrace=1:report_error_type=1
           # use_tls=0 is a workaround for LSAN crashing with "Tracer caught signal 11" (SIGSEGV),
@@ -106,6 +107,7 @@ jobs:
         sudo pip3 install pexpect
     - name: cmake
       env:
+          FISH_CI_SAN: 1
           CC: clang
           CXX: clang++
           CXXFLAGS: "-fsanitize=thread"