CI: Pin Emscripten version for reproducible builds
CI: Pin Emscripten version for reproducible builds

Emscripten is a fast-moving target which gets tons of improvements all the time,
but it's not rare that some regressions affect us and make our CI builds fail.
(See e.g. #33728, #35237, #39168, #40563, and #40914.)

Let's pin to a stable version to avoid having external factors impact our CI,
and update this version manually regularly in a PR to ensure that the new
version works well for us.

Zylann/godot,guilhermefelipecgs/godot,Zylann/godot,guilhermefelipecgs/godot,godotengine/godot,Faless/godot,godotengine/godot,sanikoyes/godot,honix/godot,vkbsb/godot,honix/godot,Faless/godot,Faless/godot,pkowal1982/godot,akien-mga/godot,MarianoGnu/godot,sanikoyes/godot,firefly2442/godot,vnen/godot,vkbsb/godot,MarianoGnu/godot,BastiaanOlij/godot,Zylann/godot,Valentactive/godot,Zylann/godot,firefly2442/godot,pkowal1982/godot,MarianoGnu/godot,BastiaanOlij/godot,MarianoGnu/godot,akien-mga/godot,josempans/godot,josempans/godot,Faless/godot,honix/godot,Paulloz/godot,pkowal1982/godot,firefly2442/godot,josempans/godot,pkowal1982/godot,DmitriySalnikov/godot,ZuBsPaCe/godot,Faless/godot,vkbsb/godot,godotengine/godot,Shockblast/godot,sanikoyes/godot,ZuBsPaCe/godot,josempans/godot,sanikoyes/godot,firefly2442/godot,Shockblast/godot,Paulloz/godot,Zylann/godot,Paulloz/godot,Shockblast/godot,BastiaanOlij/godot,Paulloz/godot,ZuBsPaCe/godot,BastiaanOlij/godot,DmitriySalnikov/godot,vnen/godot,Paulloz/godot,Valentactive/godot,Shockblast/godot,sanikoyes/godot,Paulloz/godot,MarianoGnu/godot,BastiaanOlij/godot,vnen/godot,vnen/godot,ZuBsPaCe/godot,vnen/godot,godotengine/godot,Faless/godot,vkbsb/godot,pkowal1982/godot,Faless/godot,Valentactive/godot,honix/godot,sanikoyes/godot,ZuBsPaCe/godot,Valentactive/godot,godotengine/godot,Shockblast/godot,josempans/godot,Shockblast/godot,Shockblast/godot,ZuBsPaCe/godot,Shockblast/godot,akien-mga/godot,guilhermefelipecgs/godot,pkowal1982/godot,Zylann/godot,MarianoGnu/godot,BastiaanOlij/godot,godotengine/godot,honix/godot,ZuBsPaCe/godot,guilhermefelipecgs/godot,josempans/godot,firefly2442/godot,vnen/godot,DmitriySalnikov/godot,akien-mga/godot,guilhermefelipecgs/godot,pkowal1982/godot,DmitriySalnikov/godot,akien-mga/godot,firefly2442/godot,vnen/godot,josempans/godot,akien-mga/godot,akien-mga/godot,vkbsb/godot,Zylann/godot,vkbsb/godot,sanikoyes/godot,Valentactive/godot,Paulloz/godot,guilhermefelipecgs/godot,godotengine/godot,Zylann/godot,Valentactive/godot,vkbsb/godot,sanikoyes/godot,BastiaanOlij/godot,firefly2442/godot,DmitriySalnikov/godot,josempans/godot,pkowal1982/godot,MarianoGnu/godot,BastiaanOlij/godot,Valentactive/godot,akien-mga/godot,MarianoGnu/godot,vnen/godot,Valentactive/godot,DmitriySalnikov/godot,vkbsb/godot,firefly2442/godot,honix/godot,guilhermefelipecgs/godot,ZuBsPaCe/godot,Faless/godot,godotengine/godot,DmitriySalnikov/godot,guilhermefelipecgs/godot