ci : add mirror for ports.ubuntu.com (ARM packages) (#3221)

This commit updates the build workflow to replace `ports.ubuntu.com`
with `mirror.kumi.systems` in the apt sources list for ARM64 builds.

The motivation for this change is intended to improve package download
reliability and speed by using a more stable mirror for ARM64 packages.

Author: danbev

.github/workflows/build.yml

@@ -137,6 +137,10 @@ jobs:
             sed -i "s|archive.ubuntu.com|mirrors.kernel.org|g" /etc/apt/sources.list
             sed -i "s|security.ubuntu.com|mirrors.kernel.org|g" /etc/apt/sources.list
 
+            apt-get update
+            apt-get install -y ca-certificates
+            sed -i "s|http://ports.ubuntu.com|https://mirror.kumi.systems|g" /etc/apt/sources.list
+
             apt update
             apt install -y build-essential libsdl2-dev cmake git
             cmake -B build -DGGML_NATIVE=OFF -DGGML_CPU_ARM_ARCH=armv8-a
@@ -169,6 +173,10 @@ jobs:
             sed -i "s|archive.ubuntu.com|mirrors.kernel.org|g" /etc/apt/sources.list
             sed -i "s|security.ubuntu.com|mirrors.kernel.org|g" /etc/apt/sources.list
 
+            apt-get update
+            apt-get install -y ca-certificates
+            sed -i "s|http://ports.ubuntu.com|https://mirror.kumi.systems|g" /etc/apt/sources.list
+
             apt update
             apt install -y build-essential libsdl2-dev cmake git
             cmake -B build -DGGML_NATIVE=OFF -DGGML_CPU_ARM_ARCH=armv7-a+fp
@@ -292,6 +300,10 @@ jobs:
             sed -i "s|archive.ubuntu.com|mirrors.kernel.org|g" /etc/apt/sources.list
             sed -i "s|security.ubuntu.com|mirrors.kernel.org|g" /etc/apt/sources.list
 
+            apt-get update
+            apt-get install -y ca-certificates
+            sed -i "s|http://ports.ubuntu.com|https://mirror.kumi.systems|g" /etc/apt/sources.list
+
             apt update
             apt install -y build-essential cmake libsdl2-dev git
             cmake . -DWHISPER_SDL2=ON -DCMAKE_BUILD_TYPE=${{ matrix.build }} -DGGML_NATIVE=OFF -DGGML_CPU_ARM_ARCH=armv8-a
@@ -326,6 +338,10 @@ jobs:
             sed -i "s|archive.ubuntu.com|mirrors.kernel.org|g" /etc/apt/sources.list
             sed -i "s|security.ubuntu.com|mirrors.kernel.org|g" /etc/apt/sources.list
 
+            apt-get update
+            apt-get install -y ca-certificates
+            sed -i "s|http://ports.ubuntu.com|https://mirror.kumi.systems|g" /etc/apt/sources.list
+
             apt update
             apt install -y build-essential cmake libsdl2-dev git
             cmake . -DWHISPER_SDL2=ON -DCMAKE_BUILD_TYPE=${{ matrix.build }} -DGGML_NATIVE=OFF -DGGML_CPU_ARM_ARCH=armv7-a+fp
@@ -363,6 +379,10 @@ jobs:
             sed -i "s|archive.ubuntu.com|mirrors.kernel.org|g" /etc/apt/sources.list
             sed -i "s|security.ubuntu.com|mirrors.kernel.org|g" /etc/apt/sources.list
 
+            apt-get update
+            apt-get install -y ca-certificates
+            sed -i "s|http://ports.ubuntu.com|https://mirror.kumi.systems|g" /etc/apt/sources.list
+
             apt update
             apt install -y clang build-essential cmake libsdl2-dev git
             cmake . -DWHISPER_SDL2=ON -DCMAKE_BUILD_TYPE=${{ matrix.build }} -DCMAKE_CXX_COMPILER=clang++ -DCMAKE_C_COMPILER=clang