[MWRAPPER-150] - Fails to validate checksums on MacOS Sequoia

[jon-signal]

The version of sha256sum that ships with macOS Sequoia appears to have a bug where it does not read from stdin by default, even though its man page says, in part (emphasis added):

In all cases, each file listed on the command line is processed separately. If no files are listed on the command line, or a file name is given as -, input is taken from stdin instead.

…but invoking sha256 as it appears in the mvnw script does not work as expected:

❯ echo '3d8f20ce6103913be8b52aef6d994e0c54705fb527324ceb9b835b338739c7a8  /Users/jon/REDACTED/.mvn/wrapper/maven-wrapper.jar' | sha256sum -c
usage: sha256sum [-bctwz] [files ...]

…which in turn results in a non-successful exit code, which in turn leads to a (rather alarming!) warning about a mismatched checksums and possible compromise.

Adding a - explicitly calls for sha256sum to read from stdin.

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