Fix `subscription_capacity` documenttion default value #4342

Job	Run time
check linter (ubuntu-latest / stable)	1m 23s
check feature flags (ubuntu-latest / stable)	8m 14s
check examples (ubuntu-latest / stable)	52s
check format (ubuntu-latest / nightly)	15s
check docs (ubuntu-latest / stable)	1m 11s
check licenses (ubuntu-latest / stable)	22s
check minimal versions of transitive dependencies (ubuntu-latest / stable)	27s
check minimal supported rust version (ubuntu-latest / msrv)	37s
check spelling (ubuntu-latest / nightly)	3m 31s
test (ubuntu-latest / stable)	7m 38s
test (macos-latest / stable)	8m 26s
test (windows-latest / stable)	10m 35s
	43m 31s

Provide feedback