ci: enable gc64 builds for debian-like systems

NO_DOC=ci
NO_TEST=ci
NO_CHANGELOG=ci

(cherry picked from commit 0d27174d)

.github/workflows/debian_10.yml

@@ -44,7 +44,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        gc64: [ "GC64=OFF" ]
+        gc64: [ "GC64=OFF", "GC64=ON" ]
 
     steps:
       - uses: actions/checkout@v2.3.4

.github/workflows/debian_11.yml

@@ -44,7 +44,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        gc64: [ "GC64=OFF" ]
+        gc64: [ "GC64=OFF", "GC64=ON" ]
 
     steps:
       - uses: actions/checkout@v2.3.4

.github/workflows/debian_9.yml

@@ -44,7 +44,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        gc64: [ "GC64=OFF" ]
+        gc64: [ "GC64=OFF", "GC64=ON" ]
 
     steps:
       - uses: actions/checkout@v2.3.4

.github/workflows/ubuntu_16_04.yml

@@ -44,7 +44,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        gc64: [ "GC64=OFF" ]
+        gc64: [ "GC64=OFF", "GC64=ON" ]
 
     steps:
       - uses: actions/checkout@v2.3.4

.github/workflows/ubuntu_18_04.yml

@@ -44,7 +44,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        gc64: [ "GC64=OFF" ]
+        gc64: [ "GC64=OFF", "GC64=ON" ]
 
     steps:
       - uses: actions/checkout@v2.3.4

.github/workflows/ubuntu_20_04.yml

@@ -44,7 +44,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        gc64: [ "GC64=OFF" ]
+        gc64: [ "GC64=OFF", "GC64=ON" ]
 
     steps:
       - uses: actions/checkout@v2.3.4

.github/workflows/ubuntu_21_04.yml

@@ -44,7 +44,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        gc64: [ "GC64=OFF" ]
+        gc64: [ "GC64=OFF", "GC64=ON" ]
 
     steps:
       - uses: actions/checkout@v2.3.4

.github/workflows/ubuntu_21_10.yml

@@ -44,7 +44,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        gc64: [ "GC64=OFF" ]
+        gc64: [ "GC64=OFF", "GC64=ON" ]
 
     steps:
       - uses: actions/checkout@v2.3.4