fix: Ensure protocol slashes are preserved in getSanitizedPath

[sanhee]

Description

When using WebClient with UriBuilder to construct URIs, I encountered a problem where the protocol's double slashes (://) were incorrectly reduced to a single slash (:/).
As a result, malformed URIs such as http:/jsonplaceholder.typicode.com/users were generated, causing WebClient to throw a Host is not specified exception.
This prevented the request from reaching the server and resulted in a 500 error.

This behavior occurred because the getSanitizedPath method in the UriComponentsBuilder class attempted to remove redundant slashes, but inadvertently changed the protocol structure by failing to preserve the :// delimiter.

Error Sample

org.springframework.web.reactive.function.client.WebClientRequestException: Host is not specified
	at org.springframework.web.reactive.function.client.ExchangeFunctions$DefaultExchangeFunction.lambda$wrapException$9(ExchangeFunctions.java:137) ~[spring-webflux-6.2.0.jar:6.2.0]
	Suppressed: reactor.core.publisher.FluxOnAssembly$OnAssemblyException: 
Assembly trace from producer [reactor.core.publisher.MonoErrorSupplied] :
	reactor.core.publisher.Mono.error(Mono.java:315)
	org.springframework.web.reactive.function.client.ExchangeFunctions$DefaultExchangeFunction.wrapException(ExchangeFunctions.java:137)
Error has been observed at the following site(s):
	*____________Mono.error ⇢ at org.springframework.web.reactive.function.client.ExchangeFunctions$DefaultExchangeFunction.wrapException(ExchangeFunctions.java:137)
	*____Mono.onErrorResume ⇢ at org.springframework.web.reactive.function.client.ExchangeFunctions$DefaultExchangeFunction.exchange(ExchangeFunctions.java:106)
	|_             Mono.map ⇢ at org.springframework.web.reactive.function.client.ExchangeFunctions$DefaultExchangeFunction.exchange(ExchangeFunctions.java:107)
	|_        Mono.doOnNext ⇢ at org.springframework.web.reactive.function.client.DefaultWebClient$ObservationFilterFunction.filter(DefaultWebClient.java:745)
	*____________Mono.defer ⇢ at org.springframework.web.reactive.function.client.DefaultWebClient$DefaultRequestBodyUriSpec.lambda$exchange$12(DefaultWebClient.java:467)
	|_           checkpoint ⇢ Request to GET http:/jsonplaceholder.typicode.com/users [DefaultWebClient]
	|_   Mono.switchIfEmpty ⇢ at 
...

Changes

• Refined logic to ensure protocol slashes are preserved.
• Cleaned up redundant slashes in the path without affecting the protocol.

Test

• To validate and fix this behavior, I tested the private getSanitizedPath method using reflection.
  • Since the method is private and part of an internal class, reflection was necessary to access and evaluate its behavior in isolation.
• Verified with multiple inputs, including paths with and without protocols, to ensure correct behavior.

AS-IS (Existing Issue)	TO-BE (Fixed Behavior)

Example Test Case

Input: http://example.com//path/to//resource
Output: http://example.com/path/to/resource

Input: https://example.com//path
Output: https://example.com/path

Input: example.com//path
Output: example.com/path

[sanhee]

Hi @bclozel
Hope you're well! About a month ago, I noticed that the first build for this PR failed, but I've since fixed the issue and pushed an update.
It seems that the actions need to be retriggered for the updated changes.

If you have some time, would you mind retriggering the actions?
I'd also really appreciate it if you could take a look at the changes and let me know if there's anything else I should adjust or clarify! 😊