improve next-image-proxy test

[ztanner]

This fixes a warning where the test server was exiting before all the proxy requests finished. This also throws an error to fail the test if any of the proxied requests aren't fulfilled.

slack x-ref

[ijjk]

Tests Passed

[ijjk]

Stats from current PR

Default Build

General

	vercel/next.js canary	vercel/next.js fix/https-proxy-image-test	Change
buildDuration	10.4s	10.5s	N/A
buildDurationCached	6.1s	6.3s	⚠️ +161ms
nodeModulesSize	172 MB	172 MB	✓
nextStartRea..uration (ms)	539ms	535ms	N/A

Client Bundles (main, webpack)

	vercel/next.js canary	vercel/next.js fix/https-proxy-image-test	Change
199-HASH.js gzip	27.5 kB	27.5 kB	N/A
3f784ff6-HASH.js gzip	50.9 kB	50.9 kB	✓
99.HASH.js gzip	182 B	182 B	✓
framework-HASH.js gzip	45.3 kB	45.3 kB	✓
main-app-HASH.js gzip	254 B	252 B	N/A
main-HASH.js gzip	32.9 kB	32.9 kB	N/A
webpack-HASH.js gzip	1.75 kB	1.75 kB	N/A
Overall change	96.4 kB	96.4 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	vercel/next.js fix/https-proxy-image-test	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	vercel/next.js fix/https-proxy-image-test	Change
_app-HASH.js gzip	206 B	205 B	N/A
_error-HASH.js gzip	182 B	180 B	N/A
amp-HASH.js gzip	506 B	505 B	N/A
css-HASH.js gzip	322 B	323 B	N/A
dynamic-HASH.js gzip	2.57 kB	2.57 kB	N/A
edge-ssr-HASH.js gzip	260 B	259 B	N/A
head-HASH.js gzip	350 B	350 B	✓
hooks-HASH.js gzip	369 B	369 B	✓
image-HASH.js gzip	4.35 kB	4.35 kB	N/A
index-HASH.js gzip	256 B	256 B	✓
link-HASH.js gzip	2.64 kB	2.63 kB	N/A
routerDirect..HASH.js gzip	312 B	311 B	N/A
script-HASH.js gzip	385 B	384 B	N/A
withRouter-HASH.js gzip	307 B	308 B	N/A
1afbb74e6ecf..834.css gzip	106 B	106 B	✓
Overall change	1.08 kB	1.08 kB	✓

Client Build Manifests

	vercel/next.js canary	vercel/next.js fix/https-proxy-image-test	Change
_buildManifest.js gzip	485 B	482 B	N/A
Overall change	0 B	0 B	✓

Rendered Page Sizes

	vercel/next.js canary	vercel/next.js fix/https-proxy-image-test	Change
index.html gzip	529 B	528 B	N/A
link.html gzip	542 B	541 B	N/A
withRouter.html gzip	525 B	522 B	N/A
Overall change	0 B	0 B	✓

Edge SSR bundle Size

	vercel/next.js canary	vercel/next.js fix/https-proxy-image-test	Change
edge-ssr.js gzip	93.7 kB	93.7 kB	N/A
page.js gzip	152 kB	152 kB	N/A
Overall change	0 B	0 B	✓

Middleware size

	vercel/next.js canary	vercel/next.js fix/https-proxy-image-test	Change
middleware-b..fest.js gzip	625 B	620 B	N/A
middleware-r..fest.js gzip	150 B	151 B	N/A
middleware.js gzip	22.5 kB	22.5 kB	✓
edge-runtime..pack.js gzip	1.92 kB	1.92 kB	✓
Overall change	24.4 kB	24.4 kB	✓

Commit: 723f272

[styfle]

Thanks!