[3.13] gh-120524: Avoid a Race On _PyRuntime.types.managed_static.types[i].interp_count (gh-120657)

gh-120182 added new global state (interp_count), but didn't add thread-safety for it.  This change eliminates the possible race.

(cherry picked from commit 2c66318cdc0545da37e7046533dfe74bde129d91, AKA gh-120529)

Co-authored-by: Eric Snow <ericsnowcurrently@gmail.com>