chore(instr-pg): fix imports for ESM in tests

[david-luna]

Which problem is this PR solving?

When running test-all-versions we may get an error related to ESM modules. An example

> @opentelemetry/[email protected] test
  > nyc mocha 'test/**/*.test.ts'
  
  
   Exception during run: Error: Directory import '/home/runner/work/opentelemetry-js-contrib/opentelemetry-js-contrib/packages/instrumentation-pg/src' is not supported resolving ES modules imported from /home/runner/work/opentelemetry-js-contrib/opentelemetry-js-contrib/packages/instrumentation-pg/test/pg-pool.test.ts
      at finalizeResolution (node:internal/modules/esm/resolve:262:11)
      at moduleResolve (node:internal/modules/esm/resolve:864:10)
      at defaultResolve (node:internal/modules/esm/resolve:990:11)
      at ModuleLoader.#cachedDefaultResolve (node:internal/modules/esm/loader:749:20)
      at ModuleLoader.resolve (node:internal/modules/esm/loader:726:38)
      at ModuleLoader.getModuleJobForImport (node:internal/modules/esm/loader:312:38)
      at ModuleJob.#link (node:internal/modules/esm/module_job:208:49) {
    code: 'ERR_UNSUPPORTED_DIR_IMPORT',
    url: 'file:///home/runner/work/opentelemetry-js-contrib/opentelemetry-js-contrib/packages/instrumentation-pg/src'
  }

The reason might be that the test file is considered an ESM module in a specific situations (no sure which one yet) and ESM does not accept the import of directories.

Short description of the changes

• update imports in test files

[maryliag]

looks like tests are still failing 😢

[david-luna]

looks like tests are still failing 😢

Yeah, but the error is not consistent. Sometimes I get problems loading pg module and others it complains about loading a file in the test 🤔

[david-luna]

@maryliag it's a problem in the test process. Superseded by #3017