fix(ts): fix nock @~11.0.0

[jkwlui]

Started to see typescript compilation failed overnight:

> @google-cloud/storage@3.1.0 compile /Users/jonathanlui/nodejs-storage
> tsc -p .

system-test/storage.ts:108:1 - error TS2349: Cannot invoke an expression whose type lacks a call signature. Type 'typeof import("/Users/jonathanlui/nodejs-storage/node_modules/nock/types/index")' has no compatible call signatures.

108 nock('http://metadata.google.internal')
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

There hasn't been releases to @types/nock, typescript or gts. So
this is a temporary fix to unblock releasing while we figure out why.

Update

Turns out starting at nock@11.1.0, they shipped their own typescript definition in the package. The types assumed the downstream library uses esModuleInterop so

import * as nock from 'nock' failed typescript compilation, while
import nock from 'nock' successfully compiled, but failed at runtime.

[codecov]

Codecov Report

Merging #819 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #819   +/-   ##
=======================================
  Coverage   95.05%   95.05%           
=======================================
  Files          10       10           
  Lines        1152     1152           
  Branches      288      288           
=======================================
  Hits         1095     1095           
  Misses         29       29           
  Partials       28       28

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