[swift_snapshot_tool] Use <= instead of < then when determining the tag to use for the date.

Otherwise, if one knows the specific date one wants to use, one always uses the
tag before it which is annoying.

Author: gottesmm

utils/swift_snapshot_tool/Sources/swift_snapshot_tool/bisect_toolchains.swift

@@ -95,7 +95,7 @@ struct BisectToolchains: AsyncParsableCommand {
     // just say 50 toolchains ago. To get a few weeks worth. This is easier than
     // writing dates a lot.
     let oldDateAsDate = self.oldDateAsDate
-    guard let goodTagIndex = tags.firstIndex(where: { $0.tag.date(branch: self.branch) < oldDateAsDate }) else {
+    guard let goodTagIndex = tags.firstIndex(where: { $0.tag.date(branch: self.branch) <= oldDateAsDate }) else {
       log("Failed to find tag with date: \(oldDateAsDate)")
       fatalError()
     }

utils/swift_snapshot_tool/Sources/swift_snapshot_tool/run_toolchain.swift

@@ -80,7 +80,7 @@ struct RunToolchains: AsyncParsableCommand {
     let tags = try! await getTagsFromSwiftRepo(branch: branch)
 
     let date = self.dateAsDate
-    guard var tagIndex = tags.firstIndex(where: { $0.tag.date(branch: self.branch) < date }) else {
+    guard var tagIndex = tags.firstIndex(where: { $0.tag.date(branch: self.branch) <= date }) else {
       log("Failed to find tag with date: \(date)")
       fatalError()
     }