CI: Update to gcc-13.1.0

As this is the current version of the public cross toolchains we use,
upgrade to this now.

Suggested-by: Alexey Brodkin <Alexey.Brodkin@synopsys.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
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Cc: Heinrich Schuchardt <xypron.glpk@gmx.de>

Heinrich, at this point is there a newer grub we should be testing?
There's now 2 changes for RISC-V that we're cherry-picking for newer
toolchains.