fix: pinning cdk dependencies (#18)

Something changed after `v2.103.1` which causes the action to fail with
the below error. Pin it for now.

```shell
Error performing diff:  Error: ENOENT: no such file or directory, open '/home/runner/work/_actions/corymhall/cdk-diff-action/v1-beta/db.json.gz'
    at Object.open (node:internal/fs/sync:78:18)
    at Object.openSync (node:fs:565:17)
    at readFileSync (node:fs:445:35)
    at loadAwsServiceSpecSync (/home/runner/work/_actions/corymhall/cdk-diff-action/v1-beta/node_modules/@aws-cdk/aws-service-spec/lib/index.js:44:1)
    at database (/home/runner/work/_actions/corymhall/cdk-diff-action/v1-beta/node_modules/@aws-cdk/cloudformation-diff/lib/diff/util.js:188:1)
    at loadResourceModel (/home/runner/work/_actions/corymhall/cdk-diff-action/v1-beta/node_modules/@aws-cdk/cloudformation-diff/lib/diff/util.js:198:1)
    at diffResource (/home/runner/work/_actions/corymhall/cdk-diff-action/v1-beta/node_modules/@aws-cdk/cloudformation-diff/lib/diff/index.js:39:1)
    at diffKeyedEntities (/home/runner/work/_actions/corymhall/cdk-diff-action/v1-beta/node_modules/@aws-cdk/cloudformation-diff/lib/diff/util.js:138:1)
    at Resources (/home/runner/work/_actions/corymhall/cdk-diff-action/v1-beta/node_modules/@aws-cdk/cloudformation-diff/lib/diff-template.js:30:1)
    at calculateTemplateDiff (/home/runner/work/_actions/corymhall/cdk-diff-action/v1-beta/node_modules/@aws-cdk/cloudformation-diff/lib/diff-template.js:101:1) {
  errno: -2,
  code: 'ENOENT',
  syscall: 'open',
  path: '/home/runner/work/_actions/corymhall/cdk-diff-action/v1-beta/db.json.gz'
}
```

.projenrc.ts

@@ -10,6 +10,7 @@ const project = new GitHubActionTypeScriptProject({
   name: 'cdk-diff-action',
   projenrcTs: true,
   depsUpgradeOptions: {
+    exclude: ['@aws-cdk/cloudformation-diff', '@aws-cdk/cloud-assembly-schema'],
     workflowOptions: {
       labels: ['auto-approve'],
       schedule: UpgradeDependenciesSchedule.WEEKLY,
@@ -61,8 +62,8 @@ const project = new GitHubActionTypeScriptProject({
   },
   deps: [
     '@octokit/webhooks-definitions',
-    '@aws-cdk/cloudformation-diff',
-    '@aws-cdk/cloud-assembly-schema',
+    '@aws-cdk/cloudformation-diff@v2.103.1',
+    '@aws-cdk/cloud-assembly-schema@v2.103.1',
     '@actions/exec@^1.1.1',
     '@actions/io@^1.1.3',
     '@actions/tool-cache@^2.0.0',

src/assembly.ts

@@ -1,5 +1,6 @@
 import * as path from 'path';
-import { AssemblyManifest, Manifest, ArtifactType, AwsCloudFormationStackProperties, NestedCloudAssemblyProperties, BootstrapRole } from '@aws-cdk/cloud-assembly-schema';
+import { AssemblyManifest, ArtifactType, AwsCloudFormationStackProperties, NestedCloudAssemblyProperties, BootstrapRole } from '@aws-cdk/cloud-assembly-schema/lib/cloud-assembly';
+import { Manifest } from '@aws-cdk/cloud-assembly-schema/lib/manifest';
 import * as fs from 'fs-extra';
 
 /**