[Typechain] - do not generate types when compiling test files

[ChristopherDedominici]

In the example-project, if you run pnpm hardhat3 test followed by pnpm build, the build process will fail.

The reason for this failure is that the compilation process consists of two steps:

1. Compilation of the smart contracts required for testing.
2. Compilation of the test files to execute the tests.

During the second step, the generated types from the first step are overwritten, causing the pnpm build command to fail because TypeScript can no longer locate the required types.

We need to find a solution to skip the type generation during the second step to prevent this issue.