Russia and China didn't get along even when they shared the same communist ideology. Neither Russia or China have strong reason to be allies, neither has ever shown any interest in helping each other out with each others border conflicts.
Beyond the propaganda value of an anti-American alliance, neither China or Russia has it in their interests to form a military alliance, plus Putin and Xi don't trust each other beyond trade and economic benefits.
Also Russia instead of increasing military support and sales of more sophisticated weapons they are actually cutting them off. Russia doesn't want to risk China having an advantage in any potential future conflict with Russia. Companies like Sukhoi have cut China off completely after they copied (after being denied approval) their SU-27, again there no trust.
Basically Russia and China don't trust each other enough to form a military alliance or see any advantage in it. An alliance would only be useful if either country was under risk of imminent invasion, which of course they are not.
