Perf Test: Fix on 6.0

[JasonGore]

Pull request checklist

• Addresses an existing issue: Fixes #0000
• Include a change request file using $ npm run change

Description of changes

#9550 changed the baseline tests for master. This ended up breaking 6.0 builds because the 6.0 branch hadn't been switched over to use 6.0 deploy links for its baseline tests. This PR fixes this problem.

Microsoft Reviewers: Open in CodeFlow

[msft-github-bot]

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[cliffkoh]

could probably also fix by using process.env.BUILD_HEADBRANCH or whatever the env name is, which is more resilient against this branch ever getting renamed

[msft-github-bot]

Component perf results:

Scenario	Target branch avg total (ms)	PR avg total (ms)	Target branch avg per item (ms)	PR avg per item (ms)	Is significant change	Is regression
PrimaryButton	53.219	53.122	0.532	0.531	false	false
BaseButton	30.486	29.419	0.305	0.294	false	false
NewButton	56.492	57.476	0.565	0.575	false	false
button	5.229	4.957	0.052	0.050	false	false
DetailsRows without styles	166.043	164.012	1.660	1.640	false	false
DetailsRows	167.010	165.507	1.670	1.655	false	false
Toggles	34.402	32.436	0.344	0.324	true	false
NewToggle	64.188	63.567	0.642	0.636	false	false
DocumentCardTitle with truncation	19.633	20.020	0.196	0.200	false	false

[size-auditor]

Size Auditor did not detect a change in bundle size for any component!

[JasonGore]

Thanks Cliff. I want to make more improvements on master so I'll try that change there first and then port it over. I'll merge this for now.

[cliffkoh]

The described improvement is more important in master branch. It is far less likely 6.0 will change.