Switch from sha256 to integrity in release notes

[dtolnay]

integrity is preferred because it works for both http_archive (legacy) and archive_override (bzlmod). sha256 only works for http_archive. Context: bazelbuild/bazel#20156

I confirmed that xxd and base64 commands are available in the GitHub ubuntu-20.04 runner:

and that this produces an integrity string that checks out with what Bazel wants. See dtolnay/cxx@17f46ec for a successful use of integrity with http_archive:

# WORKSPACE.bazel

http_archive(
    name = "rules_rust",
    integrity = "sha256-p2HVTknbBvhjRo5rukoTJSsb1Jno9wbaZeJ5s7y8XFI=",
    urls = ["https://github.com/bazelbuild/rules_rust/releases/download/0.36.2/rules_rust-v0.36.2.tar.gz"],
)

and dtolnay/cxx#1294 for a successful use of integrity with archive_override.

# MODULE.bazel

archive_override(
    module_name = "rules_rust",
    integrity = "sha256-p2HVTknbBvhjRo5rukoTJSsb1Jno9wbaZeJ5s7y8XFI=",
    urls = ["https://github.com/bazelbuild/rules_rust/releases/download/0.36.2/rules_rust-v0.36.2.tar.gz"],
)

sha256 does not work in archive_override.

ERROR: Traceback (most recent call last):
	File "/git/cxx/MODULE.bazel", line 5, column 17, in <toplevel>
		archive_override(
Error in archive_override: archive_override() got unexpected keyword argument 'sha256'
ERROR: Error computing the main repository mapping: error executing MODULE.bazel file for <root>

[illicitonion]

Thanks!