Cirrus-CI: temporarily disable amd64-gcc12 build/test on main

The amd64-gcc12 job is failing at present.  Unfortunately Cirrus-CI
appears to have a 100MB log limit and we exceed this before the error
is reported.  Disable the job for now until we can address the log
length issue.

See also cirruslabs/cirrus-ci-docs#1176.

Sponsored by:	The FreeBSD Foundation

.cirrus.yml

@@ -62,6 +62,7 @@ task:
       TOOLCHAIN_PKG: ${TOOLCHAIN}
   - name: amd64-gcc12 World and kernel build and boot smoke test (FreeBSD repo)
     only_if: $CIRRUS_REPO_FULL_NAME == 'freebsd/freebsd-src'
+    trigger_type: manual
     env:
       TARGET: amd64
       TARGET_ARCH: amd64