README, GitHub actions: replace yum with dnf

Author: Lukas955

.github/workflows/main.yml

@@ -33,7 +33,7 @@ jobs:
     - name: Enable additional repositories (CentOS 8)
       if: startsWith(matrix.image, 'centos:8')
       run: |
-        yum config-manager --set-enabled AppStream PowerTools
+        dnf config-manager --set-enabled AppStream PowerTools
     - name: Install dependencies  for libfds and IPFIXcol2 (CentOS)
       if: startsWith(matrix.image, 'centos')
       run: |

.github/workflows/packages.yml

@@ -102,7 +102,7 @@ jobs:
     - name: Enable additional repositories (CentOS 8)
       if: startsWith(matrix.image, 'centos:8')
       run: |
-        yum config-manager --set-enabled AppStream PowerTools
+        dnf config-manager --set-enabled AppStream PowerTools
     - name: Install dependencies for libfds and IPFIXcol2 (CentOS)
       if: startsWith(matrix.image, 'centos')
       run: |

README.rst

@@ -89,7 +89,7 @@ Second, install build dependencies of the collector
 
 .. code-block::
 
-    yum config-manager --set-enabled AppStream PowerTools
+    dnf config-manager --set-enabled AppStream PowerTools
 
 **Debian/Ubuntu:**