chore(deps-dev): bump @salesforce/cli-plugins-testkit

Bumps [@salesforce/cli-plugins-testkit](https://github.com/salesforcecli/cli-plugins-testkit) from 1.5.6 to 1.5.15.
- [Release notes](https://github.com/salesforcecli/cli-plugins-testkit/releases)
- [Changelog](https://github.com/salesforcecli/cli-plugins-testkit/blob/main/CHANGELOG.md)
- [Commits](salesforcecli/cli-plugins-testkit@v1.5.6...v1.5.15)

---
updated-dependencies:
- dependency-name: "@salesforce/cli-plugins-testkit"
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

yarn.lock

@@ -647,9 +647,9 @@
     safe-json-stringify "~1"
 
 "@salesforce/cli-plugins-testkit@^1.4.10":
-  version "1.5.6"
-  resolved "https://registry.yarnpkg.com/@salesforce/cli-plugins-testkit/-/cli-plugins-testkit-1.5.6.tgz#e2f779dab85017ccbedea8153ebd2462aa0b7dba"
-  integrity sha512-qdr5SYBK4+8Mr6j4DeryzjAFU5T0q0W2JxKt6xgzVNVr8n/8i0/kv+5Ox46ouNcFvdlhzXXbKittakc9CL3xbA==
+  version "1.5.15"
+  resolved "https://registry.yarnpkg.com/@salesforce/cli-plugins-testkit/-/cli-plugins-testkit-1.5.15.tgz#c0444bf9a44477c6d15c39d74041a5657fcc2f5b"
+  integrity sha512-AvtjEwVDo3dZFouYM2jDRgt02uQv/TXplfpRaNEUjq++14u35R5rt4D0GSnH6AHzyJ9J4O+3jU4bk9yyTfuI5A==
   dependencies:
     "@salesforce/core" "^2.24.0"
     "@salesforce/kit" "^1.5.13"