fix(lambda-nodejs): do not require a frozen lockfile for bun (#32908)

### Issue #32906

Closes #32906.

### Reason for this change

When I implemented `bun` support, I accidentally used `--frozen-lockfile`, which caused issues when the lockfile contained additional entries other than what's being bundled in the docker container.

The issue has a small repro-case.

### Description of changes

I removed the `--frozen-lockfile` flag, which resolved the problem.

### Describe any new or updated permissions being added

N/A

### Description of how you validated changes

I added an additional package to the `bun.lockb` file in the integration test. This caused the issue to occur in the test suite. Once I made the changes in this PR, the test started passing again.

### Checklist
- [x] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md)

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: blimmer

packages/@aws-cdk-testing/framework-integ/test/aws-lambda-nodejs/test/integ-handlers/bun/_package.json

@@ -0,0 +1,8 @@
+{
+  "/": "We call this _package.json so nx doesn't get confused. If you need to regenerate the lockfile, temporarily rename this file to package.json",
+  "//": "It's important to have two dependencies here (one bundled, one not) to test that the lockfile can be updated in the docker container.",
+  "dependencies": {
+    "axios": "1.7.8",
+    "express": "4.19.2"
+  }
+}

packages/@aws-cdk-testing/framework-integ/test/aws-lambda-nodejs/test/integ-handlers/bun/bun.lockb

@@ -38,7 +38,7 @@
      "S3Bucket": {
       "Fn::Sub": "cdk-hnb659fds-assets-${AWS::AccountId}-${AWS::Region}"
      },
-     "S3Key": "06377804ec21f3cc33473a6b5853b2a873177c1ebe09b176c3ab1eef45287c97.zip"
+     "S3Key": "34a0cfe827762d92939af809d39b2595744d7d29328d6ec419935ca5a9fe9116.zip"
     },
     "Handler": "index.handler",
     "Role": {
@@ -47,7 +47,7 @@
       "Arn"
      ]
     },
-    "Runtime": "nodejs20.x"
+    "Runtime": "nodejs22.x"
    },
    "DependsOn": [
     "FunctionServiceRole675BB04A"