deps: Bump `com_github_bufbuild_buf` -> 1.21.0 (#28066)

Fix #27818

Signed-off-by: Ryan Northey <ryan@synca.io>

Mirrored from https://github.com/envoyproxy/envoy @ 308627f51e9d8bdd257cbad19bead991c358b393

bazel/repository_locations.bzl

@@ -131,11 +131,11 @@ REPOSITORY_LOCATIONS_SPEC = dict(
         project_name = "buf",
         project_desc = "A new way of working with Protocol Buffers.",  # Used for breaking change detection in API protobufs
         project_url = "https://buf.build",
-        version = "1.19.0",
-        sha256 = "ff35aa96b54037d492d30a21dce8d96d47693a761487f98551d750407c27c285",
+        version = "1.21.0",
+        sha256 = "1db51318e49f12095c97866c9b5d939dfec318b50362bba8a3a9545c4cff456b",
         strip_prefix = "buf",
         urls = ["https://github.com/bufbuild/buf/releases/download/v{version}/buf-Linux-x86_64.tar.gz"],
-        release_date = "2023-05-17",
+        release_date = "2023-06-05",
         use_category = ["api"],
         license = "Apache-2.0",
         license_url = "https://github.com/bufbuild/buf/blob/v{version}/LICENSE",