test: stop running placeholder el test in IE and Safari to prevent errors

[misteroneill]

Description

We realized that tests were failing in IE11 and Safari 9 because some new tests introduced in #7722 seem to use unsupported DocumentFragment features.

Rather than try to fix that, we will simply not run these tests in IE or Safari. In 8.0, we will not support IE at all or older Safaris.

Requirements Checklist

• Feature implemented / Bug fixed
• If necessary, more likely in a feature request than a bug fix
  • Change has been verified in an actual browser (Chrome, Firefox, IE)
  • Unit Tests updated or fixed
  • Docs/guides updated
  • Example created (starter template on JSBin)
• Reviewed by Two Core Contributors

[codecov]

Codecov Report

Merging #7769 (cce7725) into main (1908422) will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #7769      +/-   ##
==========================================
- Coverage   80.94%   80.92%   -0.02%     
==========================================
  Files         116      116              
  Lines        7461     7461              
  Branches     1811     1811              
==========================================
- Hits         6039     6038       -1     
- Misses       1422     1423       +1     

Impacted Files	Coverage Δ
...rc/js/control-bar/progress-control/time-tooltip.js	82.05% <0.00%> (-2.57%)	⬇️

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[gkatsev]

We'd want to make sure to re-enable this test for safari in v8

[misteroneill]

Absolutely!