test: disable colors in test-assert-deep.js

When test/parallel/test-assert-deep.js is run with a TTY as
stdout, color codes in assertion messages cause the test to fail.
This commit disables colors when stdout is a TTY.

PR-URL: #20695
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

test/parallel/test-assert-deep.js

@@ -7,6 +7,12 @@ const { AssertionError } = assert;
 const defaultMsgStart = 'Input A expected to strictly deep-equal input B:\n' +
                         '+ expected - actual';
 
+// Disable colored output to prevent color codes from breaking assertion
+// message comparisons. This should only be an issue when process.stdout
+// is a TTY.
+if (process.stdout.isTTY)
+  process.env.NODE_DISABLE_COLORS = '1';
+
 // Template tag function turning an error message into a RegExp
 // for assert.throws()
 function re(literals, ...values) {