Gles/fix shader compilation errors

[rjonaitis]

Purpose of this PR

Fixes URP shader compilation errors during building for GLES3/GLES2 platforms https://fogbugz.unity3d.com/f/cases/1388668/

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Testing status

Manual test of building empty project with URP for Android platform with GLES3/GLES2 APIs

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Comments to reviewers

Notes for the reviewers you have assigned.

[github-actions]

Hi! This comment will help you figure out which jobs to run before merging your PR. The suggestions are dynamic based on what files you have changed.
Link to Yamato: https://unity-ci.cds.internal.unity3d.com/project/902/
Search for your PR branch using the search bar at the top, then add the following segment(s) to the end of the URL (you may need multiple tabs depending on how many packages you change)

URP
/jobDefinition/.yamato%252Fall-urp.yml%2523PR_URP_trunk
With changes to URP packages, you should also run
/jobDefinition/.yamato%2Fall-lightmapping.yml%23PR_Lightmapping_trunk

SRP Core
You could run ABV on your branch before merging your PR, but it will start A LOT of jobs. Please be responsible about it and run it only when you feel the PR is ready:
/jobDefinition/.yamato%252F_abv.yml%2523all_project_ci_trunk
Be aware that any modifications to the Core package impacts everyone in the Graphics repo so please discuss the PR with your lead.

Depending on the scope of your PR, you may need to run more jobs than what has been suggested. Please speak to your lead or a Graphics SDET (#devs-graphics-automation) if you are unsure.

[github-actions]

It appears that you made a non-draft PR!
Please convert your PR to draft (button on the right side of the page).
See the PR template for more information.
Thank you!