SpringBoot Fix R2dbcScriptDatabaseInitializerTests whenModeIsAlwaysThenStandaloneDatabaseIsInitialized on Windows

There appears to be a breaking change in H2 2.x that is affects whenModeIsAlwaysThenStandaloneDatabaseIsInitialized in R2dbcScriptDatabaseInitializerTests. We create a ConnectionFactory from a URL like this:

r2dbc:h2:file:////C:/dev/spring-projects/spring-boot/2.6.x/spring-boot-project/spring-boot/build/03fa8763-8208-4b6d-94cb-1bbf8d727aa0?options=DB_CLOSE_DELAY=-1;DB_CLOSE_ON_EXIT=FALSE

This results in an H2 ConnectionInfo with the following name:

\C:\dev\spring-projects\spring-boot\2.6.x\spring-boot-project\spring-boot\build\03fa8763-8208-4b6d-94cb-1bbf8d727aa0

With H2 1.4.x, this name is successfully normalized by ConnectionInfo but with H2 2.x the normalization fails. The leading \ is superfluous but appears to be tolerated by H2 1.4. We can fix the problem by passing in a URL that begins r2dbc:h2:file:///C:/ (3 slates after file: rather than 4).