fix(lambda): flakiness due to existing template.yaml

[vicheey]

Problem

fix #6921

Solution

Refactor the tests for cleaner creating and deletion template.yaml file.

• Scope and group tests cases based on required starting template.
• Update assertion and error message.

---

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• License: I confirm that my contribution is made under the terms of the Apache 2.0 license.

[github-actions]

• This pull request implements a feat or fix, so it must include a changelog entry (unless the fix is for an unreleased feature). Review the changelog guidelines.
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[justinmk3]

Is this CI failure unrelated to these changes?

AssertionError [ERR_ASSERTION]: Expected values to be strictly equal:

2 !== 1

    at verifyCorrectDependencyCall (/codebuild/output/src1485263156/src/github.com/aws/aws-toolkit-vscode/packages/core/src/test/shared/sam/build.test.ts:343:20)
    at Context.<anonymous> (/codebuild/output/src1485263156/src/github.com/aws/aws-toolkit-vscode/packages/core/src/test/shared/sam/build.test.ts:530:13)

      + expected - actual

      -2
      +1