test(webhooks): use an unmistakable placeholder for the token fixture

`tok_abcdefgh1234` matches a generic token pattern and tripped GitGuardian.
The value only has to be long enough to clear the value-matching threshold, so
name it for what it is.

Author: waleedlatif1

apps/sim/lib/webhooks/providers/generic.test.ts

@@ -184,18 +184,18 @@ describe('genericHandler.formatInput exposed headers', () => {
    */
   it('withholds any header carrying the configured token, whatever it is named', async () => {
     const result = await withHeaders(
-      { 'x-vendor-signature': 'tok_abcdefgh1234', 'x-event-name': 'created' },
-      { token: 'tok_abcdefgh1234' }
+      { 'x-vendor-signature': 'not-a-real-token-fixture', 'x-event-name': 'created' },
+      { token: 'not-a-real-token-fixture' }
     )
 
     expect(result.input).toEqual({ headers: { 'x-event-name': 'created' } })
   })
 
   it('withholds a header that merely embeds the token', async () => {
     const result = await withHeaders(
-      { 'x-vendor-auth': 'Token tok_abcdefgh1234' },
+      { 'x-vendor-auth': 'Token not-a-real-token-fixture' },
       {
-        token: 'tok_abcdefgh1234',
+        token: 'not-a-real-token-fixture',
       }
     )