meta: update CONTRIBUTING.md to point to test plans for skipping

[armcknight]

I noticed while double checking for #5115 (comment) that a few things were missed in #4848

Just wanted to note that there were a few skipped tests in the schemes that weren't skipped in the test plans. I don't think I've seen any of these flake so they were either fixed afterwards or they Just Work ™️ now:

• testANRButAppInBackground_NoANR
• testMultipleListeners
• testConcurrentSpansWithTimeout
• testStacktraceHasFrames_forEveryThread
• testOnMainThreadFromNonMainContext
• testDeadlineTimer_StartedAndCancelledOnMainThread

#skip-changelog

[github-actions]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	1222.94 ms	1242.53 ms	19.59 ms
Size	22.30 KiB	851.57 KiB	829.26 KiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
37fd7a2	1236.54 ms	1248.78 ms	12.23 ms
ea73af6	1230.96 ms	1244.98 ms	14.02 ms
b15521e	1238.76 ms	1250.49 ms	11.73 ms
4154aff	1225.25 ms	1244.77 ms	19.52 ms
e998fd0	1254.41 ms	1272.78 ms	18.37 ms
5616e0a	1237.00 ms	1260.43 ms	23.43 ms
7e8d5fd	1208.69 ms	1228.14 ms	19.45 ms
47b41ed	1252.31 ms	1253.96 ms	1.64 ms
7219f3b	1234.58 ms	1260.44 ms	25.85 ms
a6f8b18	1238.54 ms	1265.56 ms	27.02 ms

App size

Revision	Plain	With Sentry	Diff
37fd7a2	22.30 KiB	730.76 KiB	708.46 KiB
ea73af6	20.76 KiB	425.75 KiB	404.99 KiB
b15521e	21.58 KiB	573.17 KiB	551.58 KiB
4154aff	21.58 KiB	424.30 KiB	402.72 KiB
e998fd0	21.58 KiB	414.59 KiB	393.01 KiB
5616e0a	22.85 KiB	407.45 KiB	384.60 KiB
7e8d5fd	20.76 KiB	435.50 KiB	414.74 KiB
47b41ed	20.76 KiB	436.66 KiB	415.90 KiB
7219f3b	21.58 KiB	698.37 KiB	676.79 KiB
a6f8b18	20.76 KiB	431.87 KiB	411.11 KiB

[philprime]

LGTM, thanks.