qapi: fix colon in Since tag section

As described in docs/devel/qapi-code-gen.rst line 998,
there should be no space between "Since" and ":".

Signed-off-by: Victor Toso <victortoso@redhat.com>
Message-ID: <20241217091504.16416-1-victortoso@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

qapi/cxl.json

@@ -460,7 +460,7 @@
 #
 # @unstable: For now this command is subject to change.
 #
-# Since : 9.1
+# Since: 9.1
 ##
 { 'command': 'cxl-add-dynamic-capacity',
   'data': { 'path': 'str',
@@ -539,7 +539,7 @@
 #
 # @unstable: For now this command is subject to change.
 #
-# Since : 9.1
+# Since: 9.1
 ##
 { 'command': 'cxl-release-dynamic-capacity',
   'data': { 'path': 'str',