sql/tablemetadatacache: speed up tests

[dt]

This test was taking 35s or more before while sleeping for adoption intervals but can run in ~5s with fast adoptions.

Release note: none. Epic: none.

[cockroach-teamcity]

This change is 

[dt]

TFTR!

bors r+

[craig[bot]]

Build succeeded:

• local_roachtest
• linux_amd64_build
• local_roachtest_fips
• acceptance
• macos_amd64_build
• check_generated_code
• macos_arm64_build
• docker_image_amd64
• examples_orms
• unit_tests
• linux_arm64_build
• windows_build
• linux_amd64_fips_build
• lint