refactor(deps): remove is-error dependency

lib/assert.js

@@ -1,5 +1,4 @@
 import concordance from 'concordance';
-import isError from 'is-error';
 import isPromise from 'is-promise';
 
 import concordanceOptions from './concordance-options.js';
@@ -154,7 +153,7 @@ function validateExpectations(assertion, expectations, numberArgs) { // eslint-d
 // Note: this function *must* throw exceptions, since it can be used
 // as part of a pending assertion for promises.
 function assertExpectations({assertion, actual, expectations, message, prefix, savedError}) {
-	if (!isError(actual)) {
+	if (!(actual instanceof Error)) {
 		throw new AssertionError({
 			assertion,
 			message,

lib/serialize-error.js

@@ -4,7 +4,6 @@ import {fileURLToPath, pathToFileURL} from 'node:url';
 
 import cleanYamlObject from 'clean-yaml-object';
 import concordance from 'concordance';
-import isError from 'is-error';
 import StackUtils from 'stack-utils';
 
 import {AssertionError} from './assert.js';
@@ -146,7 +145,7 @@ function trySerializeError(error, shouldBeautifyStack, testFile) {
 }
 
 export default function serializeError(origin, shouldBeautifyStack, error, testFile) {
-	if (!isError(error)) {
+	if (!(error instanceof Error)) {
 		return {
 			avaAssertionError: false,
 			nonErrorObject: true,

package.json

@@ -96,7 +96,6 @@
 		"globby": "^12.0.2",
 		"ignore-by-default": "^2.0.0",
 		"indent-string": "^5.0.0",
-		"is-error": "^2.2.2",
 		"is-plain-object": "^5.0.0",
 		"is-promise": "^4.0.0",
 		"matcher": "^5.0.0",