chore(deps): bump koa from 2.15.3 to 2.15.4 in /examples/web-test-runner (#120)

Bumps [koa](https://github.com/koajs/koa) from 2.15.3 to 2.15.4.
- [Release notes](https://github.com/koajs/koa/releases)
- [Changelog](https://github.com/koajs/koa/blob/2.15.4/History.md)
- [Commits](koajs/koa@2.15.3...2.15.4)

---
updated-dependencies:
- dependency-name: koa
  dependency-type: indirect
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

examples/web-test-runner/yarn.lock

@@ -1745,9 +1745,9 @@ koa-static@^5.0.0:
     koa-send "^5.0.0"
 
 koa@^2.13.0:
-  version "2.15.3"
-  resolved "https://registry.yarnpkg.com/koa/-/koa-2.15.3.tgz#062809266ee75ce0c75f6510a005b0e38f8c519a"
-  integrity sha512-j/8tY9j5t+GVMLeioLaxweJiKUayFhlGqNTzf2ZGwL0ZCQijd2RLHK0SLW5Tsko8YyyqCZC2cojIb0/s62qTAg==
+  version "2.15.4"
+  resolved "https://registry.yarnpkg.com/koa/-/koa-2.15.4.tgz#7000b3d8354558671adb1ba1b1c09bedb5f8da75"
+  integrity sha512-7fNBIdrU2PEgLljXoPWoyY4r1e+ToWCmzS/wwMPbUNs7X+5MMET1ObhJBlUkF5uZG9B6QhM2zS1TsH6adegkiQ==
   dependencies:
     accepts "^1.3.5"
     cache-content-type "^1.0.0"