fix(events): eventSourceName does not accept tokens (aws#20719)

Addresses aws#20718 

Adds a check to see if the value is a token before running the validation regex on `eventSourceName`.

Simple fix following a similar fix in aws#10772

----

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packages/@aws-cdk/aws-events/lib/event-bus.ts

@@ -269,16 +269,18 @@ export class EventBus extends EventBusBase {
     }
 
     if (eventSourceName !== undefined) {
-      // Ex: aws.partner/PartnerName/acct1/repo1
-      const eventSourceNameRegex = /^aws\.partner(\/[\.\-_A-Za-z0-9]+){2,}$/;
-      if (!eventSourceNameRegex.test(eventSourceName)) {
-        throw new Error(
-          `'eventSourceName' must satisfy: ${eventSourceNameRegex}`,
-        );
-      } else if (!eventBusNameRegex.test(eventSourceName)) {
-        throw new Error(
-          `'eventSourceName' must satisfy: ${eventBusNameRegex}`,
-        );
+      if (!Token.isUnresolved(eventSourceName)) {
+        // Ex: aws.partner/PartnerName/acct1/repo1
+        const eventSourceNameRegex = /^aws\.partner(\/[\.\-_A-Za-z0-9]+){2,}$/;
+        if (!eventSourceNameRegex.test(eventSourceName)) {
+          throw new Error(
+            `'eventSourceName' must satisfy: ${eventSourceNameRegex}`,
+          );
+        } else if (!eventBusNameRegex.test(eventSourceName)) {
+          throw new Error(
+            `'eventSourceName' must satisfy: ${eventBusNameRegex}`,
+          );
+        }
       }
       return { eventBusName: eventSourceName, eventSourceName };
     }

packages/@aws-cdk/aws-events/test/event-bus.test.ts

@@ -254,6 +254,16 @@ describe('event bus', () => {
     }).toThrow(/'eventSourceName' must satisfy: \/\^aws/);
   });
 
+  test('does not throw if eventSourceName is a token', () => {
+    // GIVEN
+    const stack = new Stack();
+
+    // WHEN / THEN
+    expect(() => new EventBus(stack, 'EventBus', {
+      eventSourceName: Aws.STACK_NAME,
+    })).not.toThrow();
+  });
+
   test('event bus source name cannot be empty string', () => {
     // GIVEN
     const stack = new Stack();