integration-tests/load: fix outstanding linter issues

[jmank88]

https://github.com/smartcontractkit/chainlink/actions/runs/13777376230/job/38529222822

<checkstyle version="5.0">
  <file name="integration-tests/load/ccip/ccip_test.go">
    <error column="12" line="126" message="go-require: prepareAccountToSendLink contains assertions that must only be used in the goroutine running the test function" severity="error" source="testifylint"></error>
    <error column="5" line="133" message="go-require: require must only be used in the goroutine running the test function" severity="error" source="testifylint"></error>
  </file>
  <file name="integration-tests/load/ccip/destination_gun.go">
    <error column="21" line="141" message="G115: integer overflow conversion int64 -&gt; uint64" severity="error" source="gosec"></error>
  </file>
  <file name="integration-tests/load/ccip/helpers.go">
    <error column="2" line="163" message="unnecessary trailing newline" severity="error" source="whitespace"></error>
  </file>
</checkstyle>

[cl-sonarqube-production]

Quality Gate passed

Issues
0 New issues
0 Fixed issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

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