mesa: update to 21.1.3.

[ardadem]

General

• This is a new package and it conforms to the quality requirements

Have the results of the proposed changes been tested?

• I use the packages affected by the proposed changes on a regular basis and confirm this PR works for me
• I generally don't use the affected packages but briefly tested this PR

EDIT: tested on x86_64

[ardadem]

aarch64 failed on fetching distfile:

=> mesa-21.1.2_1: fetching distfile 'mesa-21.1.2.tar.xz'...
https://mesa.freedesktop.org/archive/mesa-21.1.2.tar.xz: Transient resolver failure
=> ERROR: mesa-21.1.2_1: failed to fetch mesa-21.1.2.tar.xz.
Error: Process completed with exit code 1.

[Cloudef]

Linking issue #30821 as this will fix it

[ardadem]

21.1.3 will be released soon, i'll update it when it's out

[tsujp]

I've been using this for the past week or so, 21.1.2 and am building 21.1.3 from this PR. It fixed some horrific artifacting I was getting with an AMD RX 6700 XT when using 21.0.3_4.

[ericonr]

21.1.4 is out, I'm build testing that and will push it if everything seems fine.

[tsujp]

How does merging this branch in work? I obviously haven't contributed here and don't want to appear as the canonical "pls merge free work now!!!!" but it appears the checks pass and I and the author have been using this with stability, what else is blocking a merge into main?