ci: increase MatrixOne memory limit

[loveRhythm1990]

What type of PR is this?

• feat (new feature)
• fix (bug fix)
• docs (documentation)
• style (formatting, no code change)
• refactor (code change that neither fixes a bug nor adds a feature)
• perf (performance improvement)
• test (adding or updating tests)
• chore (maintenance, tooling)
• build / ci (build or CI changes)

Which issue(s) this PR fixes

N/A

What this PR does / why we need it

Increase the MatrixOne service container memory limit from 2 GiB to 4 GiB in both database-test workflows.

The failed DB Tests job repeatedly reported available-mem=0 and OOM alerts while MatrixOne RSS reached the 2 GiB cgroup limit. The first graph test then lost its database connection with an unexpected EOF, and all subsequent graph tests timed out waiting for MatrixOne.

Failing job: https://github.com/matrixorigin/Memoria/actions/runs/31790266225/job/94735735526

The public Ubuntu runner has 16 GB RAM, so a 4 GiB service limit leaves sufficient capacity for Cargo and the remaining job processes.

Validation:

• actionlint passed for both modified workflows
• git diff --check passed