Fix typos (#7371)

Author: szakarias

app/lib/account/backend.dart

@@ -582,7 +582,7 @@ class AccountBackend {
   /// Returns the [UserSession] associated with the [sessionId] or
   /// `null` if it does not exists.
   ///
-  /// Deletes the session entry if is has already expired and
+  /// Deletes the session entry if it has already expired and
   /// clears the related cache too.
   Future<UserSession?> lookupValidUserSession(String sessionId) async {
     final key = _db.emptyKey.append(UserSession, id: sessionId);

app/lib/frontend/request_context.dart

@@ -38,7 +38,7 @@ class RequestContext {
   /// The parsed experimental flags.
   final ExperimentalFlags experimentalFlags;
 
-  /// The CSRF token recieved via the header of the request.
+  /// The CSRF token received via the header of the request.
   final String? csrfToken;
 
   final SessionData? sessionData;

app/lib/package/backend.dart

@@ -815,7 +815,7 @@ class PackageBackend {
       throw PackageRejectedException.uploadRestricted();
     }
     _logger.info('Starting async upload.');
-    // NOTE: We use a authenticated user scope here to ensure the uploading
+    // NOTE: We use an authenticated user scope here to ensure the uploading
     // user is authenticated. But we're not validating anything at this point
     // because we don't even know which package or version is going to be
     // uploaded.

app/lib/shared/exceptions.dart

@@ -269,7 +269,7 @@ class PackageRejectedException extends ResponseException {
       : super._(400, 'PackageRejected',
             'Version $version of package $package was deleted previously, re-upload is not allowed.');
 
-  /// The package is has an active `isBlocked` flag, no further version is allowed.
+  /// The package has an active `isBlocked` flag, no further version is allowed.
   PackageRejectedException.isBlocked()
       : super._(400, 'PackageRejected', 'Package has been blocked.');
 

pkg/indexed_blob/lib/indexed_blob.dart

@@ -289,7 +289,7 @@ class BlobIndex {
     }
     final blobId = r.expectString();
 
-    // Expect a index key
+    // Expect an index key
     if (!_skipUntilKey(r, 'index')) {
       throw const FormatException('expected "index" key');
     }
@@ -328,7 +328,7 @@ class BlobIndex {
     }
     final blobId = r.expectString();
 
-    // Expect a index key
+    // Expect an index key
     if (!_skipUntilKey(r, 'index')) {
       throw const FormatException('expected "index" key');
     }
@@ -372,7 +372,7 @@ class BlobIndex {
     }
     final originalBlobId = r.expectString();
 
-    // Expect a index key
+    // Expect an index key
     if (!_skipUntilKey(r, 'index')) {
       throw const FormatException('expected "index" key');
     }