test: skip tests related to CI failures on AIX

These tests seem to trigger failures in the entire CI job (not just the
test) on AIX. Skip them to see if that helps alleviate spurious failures
in node-test-commit-aix (and the upstream PR and commit test jobs).

See:
- nodejs/build#1820 (comment)
- nodejs/build#1847 (comment)

test/addons/stringbytes-external-exceed-max/test-stringbytes-external-exceed-max.js

@@ -5,6 +5,11 @@ const skipMessage = 'intensive toString tests due to memory confinements';
 if (!common.enoughTestMem)
   common.skip(skipMessage);
 
+// See https://github.com/nodejs/build/issues/1820#issuecomment-505998851
+// See https://github.com/nodejs/node/pull/28469
+if (process.platform === 'aix')
+  common.skip('flaky on AIX');
+
 const binding = require(`./build/${common.buildType}/binding`);
 
 // v8 fails silently if string length > v8::String::kMaxLength

test/message/message.status

@@ -16,3 +16,6 @@ prefix message
 
 [$system==freebsd]
 
+[$system==aix]
+# https://github.com/nodejs/node/pull/28469
+vm_dont_display_syntax_error: SKIP

test/pseudo-tty/pseudo-tty.status

@@ -1,6 +1,10 @@
 prefix pseudo-tty
 
 [$system==aix]
+# https://github.com/nodejs/build/issues/1820#issuecomment-505998851
+# https://github.com/nodejs/node/pull/28469
+console-dumb-tty: SKIP
+test-fatal-error: SKIP
 
 [$system==solaris]
 # https://github.com/nodejs/node/pull/16225 - `ioctl(fd, TIOCGWINSZ)` seems