fix(next_core): align remove trailing slash

[kwonoj]

What

minor fix to match behavior to https://github.com/vercel/next.js/blob/ae10b5c82b29b3b077378f05f75eb1b215b327f0/packages/next/src/shared/lib/router/utils/remove-trailing-slash.ts#L2C4-L9

as we're seeing a panic when route is /

Panic: PanicInfo { payload: Any { .. }, message: Some(byte index 1 is out of bounds of ``), location: Location { file: "packages/next-swc/crates/next-core/src/next_edge/route_regex.rs", line: 202, col: 59 }, can_unwind: true, force_no_backtrace: false }
Backtrace:    0: backtrace::backtrace::libunwind::trace

Closes WEB-1841

[ijjk]

Tests Passed

[ijjk]

Stats from current PR

Default Build

General

	vercel/next.js canary	vercel/next.js fix-trailing-slash	Change
buildDuration	10.3s	10.3s	N/A
buildDurationCached	6s	6s	N/A
nodeModulesSize	175 MB	175 MB	✓
nextStartRea..uration (ms)	401ms	397ms	N/A

Client Bundles (main, webpack)

	vercel/next.js canary	vercel/next.js fix-trailing-slash	Change
199-HASH.js gzip	32.3 kB	32.3 kB	N/A
3f784ff6-HASH.js gzip	53.2 kB	53.2 kB	N/A
99.HASH.js gzip	182 B	182 B	✓
framework-HASH.js gzip	45.5 kB	45.5 kB	✓
main-app-HASH.js gzip	254 B	252 B	N/A
main-HASH.js gzip	35.3 kB	35.4 kB	N/A
webpack-HASH.js gzip	1.75 kB	1.75 kB	N/A
Overall change	45.7 kB	45.7 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	vercel/next.js fix-trailing-slash	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-trailing-slash	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	2.59 kB	2.59 kB	✓
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	4.38 kB	4.38 kB	N/A
index-HASH.js gzip	256 B	256 B	✓
link-HASH.js gzip	2.67 kB	2.67 kB	N/A
routerDirect..HASH.js gzip	316 B	318 B	N/A
script-HASH.js gzip	385 B	384 B	N/A
withRouter-HASH.js gzip	319 B	319 B	✓
1afbb74e6ecf..834.css gzip	106 B	106 B	✓
Overall change	3.99 kB	3.99 kB	✓

Client Build Manifests

	vercel/next.js canary	vercel/next.js fix-trailing-slash	Change
_buildManifest.js gzip	484 B	482 B	N/A
Overall change	0 B	0 B	✓

Rendered Page Sizes

	vercel/next.js canary	vercel/next.js fix-trailing-slash	Change
index.html gzip	528 B	531 B	N/A
link.html gzip	542 B	542 B	✓
withRouter.html gzip	524 B	524 B	✓
Overall change	1.07 kB	1.07 kB	✓

Edge SSR bundle Size

	vercel/next.js canary	vercel/next.js fix-trailing-slash	Change
edge-ssr.js gzip	96 kB	96 kB	N/A
page.js gzip	139 kB	139 kB	N/A
Overall change	0 B	0 B	✓

Middleware size

	vercel/next.js canary	vercel/next.js fix-trailing-slash	Change
middleware-b..fest.js gzip	623 B	625 B	N/A
middleware-r..fest.js gzip	150 B	151 B	N/A
middleware.js gzip	25.8 kB	25.8 kB	N/A
edge-runtime..pack.js gzip	1.92 kB	1.92 kB	✓
Overall change	1.92 kB	1.92 kB	✓

Commit: 85aeb50

[kwonoj]

this test never passed actually:

the assertion is to check if rendered page does not have a string (

next.js/test/integration/react-18/test/index.test.js

Line 26 in 7aef93d

expect(context.stderr).not.toContain('not exist in this version')

), so the current rendered page passes since it is a error overlay with panic message only.