ci: Skip unit tests on some platforms

For some reason, running unit tests in CI gives the following on
Android:

```text
2024-11-23T02:17:49.1406378Z      Running unittests src/lib.rs (target/i686-linux-android/debug/deps/libc-79430fca1af8b7ec)
2024-11-23T02:17:49.1432206Z * daemon not running; starting now at tcp:5037
2024-11-23T02:17:52.1460169Z * daemon started successfully
2024-11-23T02:18:00.1454112Z adb: error: failed to copy '/checkout/target/i686-linux-android/debug/deps/libc-79430fca1af8b7ec' to '/data/local/tmp/libc-79430fca1af8b7ec': remote secure_mkdirs failed: Read-only file system
2024-11-23T02:18:00.1457084Z /checkout/target/i686-linux-android/debug/deps/libc-79430fca1af8b7ec: 1 file pushed, 0 skipped. 19.3 MB/s (5418952 bytes in 0.267s)
2024-11-23T02:18:00.3757282Z thread 'main' panicked at /tmp/runtest.rs:26:5:
2024-11-23T02:18:00.3758028Z assertion failed: status.success()
2024-11-23T02:18:00.3758589Z stack backtrace:
2024-11-23T02:18:00.3810307Z    0: rust_begin_unwind
2024-11-23T02:18:00.3811230Z              at /rustc/a47555110cf09b3ed59811d9b02235443e76a595/library/std/src/panicking.rs:665:5
2024-11-23T02:18:00.3812225Z    1: core::panicking::panic_fmt
2024-11-23T02:18:00.3813089Z              at /rustc/a47555110cf09b3ed59811d9b02235443e76a595/library/core/src/panicking.rs:76:14
2024-11-23T02:18:00.3814034Z    2: core::panicking::panic
2024-11-23T02:18:00.3814860Z              at /rustc/a47555110cf09b3ed59811d9b02235443e76a595/library/core/src/panicking.rs:148:5
2024-11-23T02:18:00.3815756Z    3: runtest::main
2024-11-23T02:18:00.3816545Z    4: core::ops::function::FnOnce::call_once
2024-11-23T02:18:00.3817848Z note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
2024-11-23T02:18:00.3822763Z error: test failed, to rerun pass `--lib`
```
And on s390x:

```
 + grep -Ev ^\[
KASLR disabled: CPU has no PRNG
/prog: /lib/s390x-linux-gnu/libm.so.6: version `GLIBC_2.38' not found (required by /prog)
+ grep -E (PASSED)|(test result: ok) output
/prog: /lib/s390x-linux-gnu/libc.so.6: version `GLIBC_2.39' not found (required by /prog)
error: test failed, to rerun pass `--lib`
```

For now, don't run unit tests on these platforms.

(backport <#4134>)
(cherry picked from commit f5fdb56)

ci/run.sh

@@ -83,7 +83,13 @@ fi
 cmd="cargo test --target $target ${LIBC_CI_ZBUILD_STD+"-Zbuild-std"}"
 
 # Run tests in the `libc` crate
-$cmd
+case "$target" in
+    # FIXME(android): unit tests fail to start on Android
+    # FIXME(s390x): unit tests fail to locate glibc
+    *android*) ;;
+    *s390x*) ;;
+    *) $cmd
+esac
 
 # Everything else is in `libc-test`
 cmd="$cmd --manifest-path libc-test/Cargo.toml"