fmt: Bump 9.1.0 -> 10.0.0

This matches the current yocto version.

Change-Id: I10f36903675cb32b3b4630e499dc0ccd72a64e4d
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/scripts/build-unit-test-docker b/scripts/build-unit-test-docker
index fe9bdaf..52a4900 100755
--- a/scripts/build-unit-test-docker
+++ b/scripts/build-unit-test-docker
@@ -117,7 +117,7 @@
         ],
     ),
     "fmtlib/fmt": PackageDef(
-        rev="9.1.0",
+        rev="10.0.0",
         build_type="cmake",
         config_flags=[
             "-DFMT_DOC=OFF",