🏗 Ignore markdown templates in link checker by convention (#25226)
🏗 Ignore markdown templates in link checker by convention (#25226)

Also some modernizing and cleanup.

(Offshoot of #25164)
dotandads/amphtml,jridgewell/amphtml,jridgewell/amphtml,zhangsu/amphtml,lannka/amphtml,Gregable/amphtml,tlong2/amphtml,mhc-gh/amphtml,yandex-pcode/amphtml,danielrozenberg/amphtml,erwinmombay/amphtml,src-code/amphtml,tlong2/amphtml,sharethrough/amphtml,yandex-pcode/amphtml,ampproject/amphtml,cory-work/amphtml,zhangsu/amphtml,jridgewell/amphtml,danielrozenberg/amphtml,cory-work/amphtml,rsimha-amp/amphtml,nexxtv/amphtml,danielrozenberg/amphtml,Gregable/amphtml,taboola/amphtml,sharethrough/amphtml,adup-tech/amphtml,zhangsu/amphtml,src-code/amphtml,jridgewell/amphtml,media-net/amphtml,jpettitt/amphtml,ampproject/amphtml,ampproject/amphtml,prateekbh/amphtml,mhc-gh/amphtml,Gregable/amphtml,jpettitt/amphtml,smartadserver/amphtml,adup-tech/amphtml,jpettitt/amphtml,alanorozco/amphtml,nexxtv/amphtml,zhouyx/amphtml,jridgewell/amphtml,smartadserver/amphtml,src-code/amphtml,jmadler/amphtml,alanorozco/amphtml,erwinmombay/amphtml,Gregable/amphtml,sharethrough/amphtml,danielrozenberg/amphtml,jmadler/amphtml,taboola/amphtml,yandex-pcode/amphtml,mhc-gh/amphtml,cory-work/amphtml,ampproject/amphtml,lannka/amphtml,Gregable/amphtml,prateekbh/amphtml,tlong2/amphtml,lannka/amphtml,nexxtv/amphtml,taboola/amphtml,prateekbh/amphtml,voyagegroup/amphtml,erwinmombay/amphtml,ampproject/amphtml,alanorozco/amphtml,voyagegroup/amphtml,dotandads/amphtml,honeybadgerdontcare/amphtml,sharethrough/amphtml,voyagegroup/amphtml,lannka/amphtml,zhangsu/amphtml,media-net/amphtml,jpettitt/amphtml,nexxtv/amphtml,yandex-pcode/amphtml,mhc-gh/amphtml,taboola/amphtml,media-net/amphtml,zhangsu/amphtml,rsimha-amp/amphtml,voyagegroup/amphtml,cory-work/amphtml,jmadler/amphtml,honeybadgerdontcare/amphtml,smartadserver/amphtml,voyagegroup/amphtml,dotandads/amphtml,zhouyx/amphtml,jpettitt/amphtml,smartadserver/amphtml,src-code/amphtml,jridgewell/amphtml,mhc-gh/amphtml,rsimha-amp/amphtml,media-net/amphtml,rsimha-amp/amphtml,honeybadgerdontcare/amphtml,mhc-gh/amphtml,honeybadgerdontcare/amphtml,smartadserver/amphtml,jmadler/amphtml,alanorozco/amphtml,dotandads/amphtml,prateekbh/amphtml,tlong2/amphtml,alanorozco/amphtml,honeybadgerdontcare/amphtml,dotandads/amphtml,zhouyx/amphtml,taboola/amphtml,sharethrough/amphtml,yandex-pcode/amphtml,mhc-gh/amphtml,rsimha-amp/amphtml,alanorozco/amphtml,danielrozenberg/amphtml,adup-tech/amphtml,media-net/amphtml,danielrozenberg/amphtml,dotandads/amphtml,nexxtv/amphtml,zhouyx/amphtml,src-code/amphtml,prateekbh/amphtml,voyagegroup/amphtml,lannka/amphtml,lannka/amphtml,ampproject/amphtml,zhouyx/amphtml,cory-work/amphtml,jpettitt/amphtml,jmadler/amphtml,erwinmombay/amphtml,sharethrough/amphtml,nexxtv/amphtml,ampproject/amphtml,erwinmombay/amphtml,Gregable/amphtml,media-net/amphtml,nexxtv/amphtml,prateekbh/amphtml,mhc-gh/amphtml,Gregable/amphtml,rsimha-amp/amphtml,jmadler/amphtml,yandex-pcode/amphtml,cory-work/amphtml,jpettitt/amphtml,honeybadgerdontcare/amphtml,zhouyx/amphtml,voyagegroup/amphtml,media-net/amphtml,honeybadgerdontcare/amphtml,alanorozco/amphtml,taboola/amphtml,jridgewell/amphtml,zhouyx/amphtml,adup-tech/amphtml,smartadserver/amphtml,adup-tech/amphtml,prateekbh/amphtml,ampproject/amphtml,cory-work/amphtml,media-net/amphtml,Gregable/amphtml,tlong2/amphtml,zhangsu/amphtml,danielrozenberg/amphtml,tlong2/amphtml,lannka/amphtml,taboola/amphtml,erwinmombay/amphtml,alanorozco/amphtml,jpettitt/amphtml,rsimha-amp/amphtml,yandex-pcode/amphtml,src-code/amphtml,danielrozenberg/amphtml,adup-tech/amphtml