[2.x] fix: trim whitespace from sbt.version in build.properties (#8524)

When sbt.version in build.properties has trailing whitespace,
sbt incorrectly reports a version mismatch even after reboot.

This fix trims the property value in all places where sbt.version
is read from build.properties:
- Main.scala (version mismatch warning)
- MainLoop.scala (clean command version detection)
- ScriptedTests.scala (test compatibility check)

Fixes #8103

main/src/main/scala/sbt/Main.scala

@@ -933,7 +933,7 @@ object BuiltinCommands {
     val sbtVersionBuildOpt = if (buildProps.exists) {
       val buildProperties = new Properties()
       IO.load(buildProperties, buildProps)
-      Option(buildProperties.getProperty(sbtVersionProperty))
+      Option(buildProperties.getProperty(sbtVersionProperty)).map(_.trim)
     } else None
 
     val sbtVersionOpt = sbtVersionSystemOpt.orElse(sbtVersionBuildOpt)

main/src/main/scala/sbt/MainLoop.scala

@@ -99,7 +99,7 @@ private[sbt] object MainLoop:
     val sbtVersionOpt = if (buildProps.exists) {
       val buildProperties = new Properties()
       IO.load(buildProperties, buildProps)
-      Option(buildProperties.getProperty("sbt.version"))
+      Option(buildProperties.getProperty("sbt.version")).map(_.trim)
     } else None
     val sbtVersion = sbtVersionOpt.getOrElse(appId.version)
     val currentArtDirs = defaultBoot * "*" / appId.groupID / appId.name / sbtVersion

scripted-sbt/src/main/scala/sbt/scriptedtest/ScriptedTests.scala

@@ -676,7 +676,7 @@ class ScriptedRunner {
 
     IO.load(buildProperties, buildPropertiesFile)
 
-    Option(buildProperties.getProperty("sbt.version")) match {
+    Option(buildProperties.getProperty("sbt.version")).map(_.trim) match {
       case Some(version) => binarySbtVersion(version) == binarySbtVersion(sbtVersion)
       case None          => true
     }