Fix compile warnings

Author: Kyle-Ye

Sources/SourceControl/GitRepository.swift

@@ -484,7 +484,7 @@ public final class GitRepository: Repository, WorkingCheckout {
     ///   - url: The new url of the remote.
     public func setURL(remote: String, url: String) throws {
         // use barrier for write operations
-        try self.lock.withLock {
+        _ = try self.lock.withLock {
             try callGit(
                 "remote",
                 "set-url",
@@ -714,7 +714,7 @@ public final class GitRepository: Repository, WorkingCheckout {
             throw InternalError("This operation is only valid in a working repository")
         }
         // use barrier for write operations
-        try self.lock.withLock {
+        _ = try self.lock.withLock {
             try callGit(
                 "checkout",
                 "-b",
@@ -729,7 +729,7 @@ public final class GitRepository: Repository, WorkingCheckout {
             throw InternalError("This operation is only valid in a working repository")
         }
 
-        try self.lock.withLock {
+        _ = try self.lock.withLock {
             try callGit(
                 "archive",
                 "--format",